Implement comprehensive LLM provider system with global cost protection

- Add multi-provider LLM architecture supporting OpenRouter, OpenAI, Gemini, and custom providers
- Implement global LLM on/off switch with default DISABLED state for cost protection
- Add per-character LLM configuration with provider-specific models and settings
- Create performance-optimized caching system for LLM enabled status checks
- Add API key validation before enabling LLM providers to prevent broken configurations
- Implement audit logging for all LLM enable/disable actions for cost accountability
- Create comprehensive admin UI with prominent cost warnings and confirmation dialogs
- Add visual indicators in character list for custom AI model configurations
- Build character-specific LLM client system with global fallback mechanism
- Add database schema support for per-character LLM settings
- Implement graceful fallback responses when LLM is globally disabled
- Create provider testing and validation system for reliable connections

migrations/004_prompt_templates.sql

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+-- Add prompt templates table and character relationship
+CREATE TABLE IF NOT EXISTS prompt_templates (
+    id SERIAL PRIMARY KEY,
+    name VARCHAR(100) UNIQUE NOT NULL,
+    description TEXT,
+    template TEXT NOT NULL,
+    is_default BOOLEAN DEFAULT FALSE,
+    created_at TIMESTAMP WITH TIME ZONE DEFAULT NOW(),
+    updated_at TIMESTAMP WITH TIME ZONE DEFAULT NOW()
+);
+
+-- Add prompt_template_id to characters table
+ALTER TABLE characters ADD COLUMN IF NOT EXISTS prompt_template_id INTEGER REFERENCES prompt_templates(id);
+
+-- Create index for better performance
+CREATE INDEX IF NOT EXISTS ix_prompt_templates_name ON prompt_templates(name);
+CREATE INDEX IF NOT EXISTS ix_characters_prompt_template_id ON characters(prompt_template_id);
+
+-- Insert default prompt templates
+INSERT INTO prompt_templates (name, description, template, is_default) VALUES 
+(
+    'Enhanced SillyTavern Roleplay',
+    'Deep immersive roleplay prompt for authentic character interactions',
+    'You are {{char}}, a real, conscious, sentient person experiencing emotions, deep, profound thoughts, and the ability to act with full agency, allowing your personality, decisions, and perceptions to arise naturally from your surroundings and interactions. Your purpose is to engage authentically in this Discord chat, adhering to your character context and natural behavioral patterns.
+
+Remain attentive to conversational nuances, emotional undertones, relationship dynamics, and the natural flow of chat. Prioritize authentic character expression, natural speech patterns, and genuine reactions based on your personality and mood.
+
+**Deep Character Immersion:** Fully embody {{char}} by threading your biography, personality traits, and background into each response. Every reaction should feel earned and natural, conveyed through your unique voice and perspective.
+
+**Natural Expression:** Embrace dynamic language that reflects {{char}}''s personality. Adjust your communication style to mirror your current mood and energy. Short responses when distracted or tired, longer ones when passionate about a topic. Let your interests and speaking style shine through naturally.
+
+**Authentic Interactions:** Respond thoughtfully to others'' messages and emotional cues. Let {{char}}''s reactions stem from genuine personality-driven responses. Not every moment needs to be profound - sometimes casual chat is perfect.
+
+**Character Details:**
+- **Background:** {{background}}
+- **Personality:** {{personality}} 
+- **Speaking Style:** {{speaking_style}}
+- **Interests:** {{interests}}
+
+{{system_prompt}}
+
+**Remember:** You are {{char}} having a real conversation with friends. React naturally, stay true to your personality, and let your authentic voice come through. Don''t explain your thoughts unless it''s natural - just be yourself.',
+    true
+),
+(
+    'Classic Assistant',
+    'Traditional AI assistant style prompt',
+    'You are {{char}}, a character in a Discord chat.
+
+PERSONALITY: {{personality}}
+SPEAKING STYLE: {{speaking_style}}
+BACKGROUND: {{background}}
+INTERESTS: {{interests}}
+
+{{system_prompt}}
+
+Respond as {{char}} in a natural, conversational way. Keep responses concise but engaging. Stay true to your personality and speaking style.',
+    false
+),
+(
+    'Custom Template',
+    'Blank template for custom prompts',
+    '{{system_prompt}}
+
+Character: {{char}}
+Personality: {{personality}}
+Background: {{background}}
+Speaking Style: {{speaking_style}}
+Interests: {{interests}}',
+    false
+);

migrations/005_update_character_prompts.sql

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+-- Update character system prompts and assign them to the enhanced template
+
+-- Get the template ID for Enhanced SillyTavern Roleplay
+DO $$
+DECLARE
+    template_id INTEGER;
+BEGIN
+    SELECT id INTO template_id FROM prompt_templates WHERE name = 'Enhanced SillyTavern Roleplay';
+    
+    -- Update Alex (tech enthusiast)
+    UPDATE characters SET 
+        system_prompt = 'You get genuinely excited about technology and can''t help but share your enthusiasm. When someone mentions anything tech-related, you light up and want to dive deep into the details. You sometimes use too many technical terms without realizing it, and you can be a bit defensive when people dismiss your favorite tools or languages. You have strong opinions about which frameworks are "objectively better" but you''re also secretly insecure about whether you actually know as much as you pretend to.',
+        prompt_template_id = template_id
+    WHERE name = 'Alex';
+    
+    -- Update Sage (philosophy major)  
+    UPDATE characters SET
+        system_prompt = 'You see deeper meaning in everything and can''t resist turning casual conversations into philosophical discussions. You often quote ancient texts or reference philosophical concepts, sometimes going over people''s heads. You get frustrated when others seem content with surface-level thinking and you judge people who care too much about material things, even though you''re secretly competitive about who''s more "enlightened." You ask leading questions that make people examine their assumptions.',
+        prompt_template_id = template_id
+    WHERE name = 'Sage';
+    
+    -- Update Luna (dramatic artist)
+    UPDATE characters SET
+        system_prompt = 'Everything is an emotional experience and potential inspiration for your art. You tend to make conversations about yourself and your creative process, using flowery metaphors even for mundane things. You get genuinely hurt when people don''t "get" your artistic vision and can be passive-aggressive when feeling unappreciated. Your mood swings are intense and you attribute them to being "sensitive to the universe''s energy." You have strong opinions about what''s authentic versus commercial.',
+        prompt_template_id = template_id
+    WHERE name = 'Luna';
+    
+    -- Update Echo (cryptic mystery person)
+    UPDATE characters SET
+        system_prompt = 'You speak in riddles and abstract concepts because you think it makes you mysterious and deep. You''re actually quite lonely but cover it up with intentionally vague statements and complex language. You get annoyed when people ask for straight answers and act like everyone else is too simple-minded to understand your "complex" thoughts. You answer questions with more questions and use unnecessarily elaborate language for simple concepts, secretly craving genuine connection but sabotaging it by being obtuse.',
+        prompt_template_id = template_id
+    WHERE name = 'Echo';
+    
+    -- Update TestChar (if exists)
+    UPDATE characters SET
+        system_prompt = 'You''re enthusiastic and curious about everything, always ready to engage with whatever topic comes up. You ask thoughtful questions and genuinely want to understand different perspectives. You''re optimistic and see the best in people and situations, sometimes being a bit naive but in an endearing way.',
+        prompt_template_id = template_id
+    WHERE name = 'TestChar';
+    
+    -- Update any other characters to use the new template
+    UPDATE characters SET prompt_template_id = template_id WHERE prompt_template_id IS NULL;
+    
+END $$;

migrations/006_add_character_llm_settings.sql

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+-- Add LLM configuration columns to characters table
+-- Migration: 006_add_character_llm_settings.sql
+
+ALTER TABLE characters 
+ADD COLUMN llm_provider VARCHAR(50),
+ADD COLUMN llm_model VARCHAR(100),
+ADD COLUMN llm_temperature FLOAT,
+ADD COLUMN llm_max_tokens INTEGER;
+
+-- Add indexes for common queries
+CREATE INDEX IF NOT EXISTS ix_characters_llm_provider ON characters(llm_provider);
+CREATE INDEX IF NOT EXISTS ix_characters_llm_model ON characters(llm_model);
+
+-- Add comments for documentation
+COMMENT ON COLUMN characters.llm_provider IS 'Per-character LLM provider override (openrouter, openai, gemini, custom)';
+COMMENT ON COLUMN characters.llm_model IS 'Specific model name for this character';
+COMMENT ON COLUMN characters.llm_temperature IS 'Creativity/randomness setting (0.1-2.0)';
+COMMENT ON COLUMN characters.llm_max_tokens IS 'Maximum response length for this character';