feat: add streaming responses with optional toggle

- Add server-sent events (SSE) streaming support for real-time token display
- Implement progressive markdown rendering during streaming
- Add stream toggle in API settings (defaults to disabled for compatibility)
- Add visual streaming indicator with pulsing animation
- Graceful fallback to non-streaming mode when disabled
- Fix character saving bug (camelCase parameter naming)

Backend changes:
- New chat_stream command with SSE parsing
- Added futures and bytes dependencies
- Emit chat-token events progressively to frontend
- Support for OpenAI-compatible and Anthropic streaming formats

Frontend changes:
- Dual code paths for streaming/non-streaming
- Real-time markdown and syntax highlighting during streaming
- Stream status indicator with animation

src-tauri/Cargo.toml

@@ -22,7 +22,9 @@ tauri = { version = "2", features = [] }
 tauri-plugin-opener = "2"
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"
-reqwest = { version = "0.12", features = ["json"] }
+reqwest = { version = "0.12", features = ["json", "stream"] }
 tokio = { version = "1", features = ["full"] }
 uuid = { version = "1", features = ["v4"] }
+futures = "0.3"
+bytes = "1"