feat: add keyboard shortcuts and copy message buttons

Keyboard shortcuts:
- Up Arrow: Edit last user message (when input at start)
- Left/Right Arrow: Navigate swipes (when not in input)
- Escape: Close panels/modals, cancel editing
- Ctrl+K: Focus message input
- Ctrl+/: Toggle Roleplay Tools
- Ctrl+Enter: Send message (alternative)

Message controls:
- Add Copy Message button for both user and assistant messages
- Visual feedback (checkmark) after copying
- 2-second feedback duration

Updated README to reflect actual implemented shortcuts.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

README.md

@@ -57,8 +57,12 @@ Config stored in `~/.config/claudia/config.json`
 
 - **Enter** - Send message
 - **Shift+Enter** - New line
-- **Up Arrow** - Edit last user message
-- **Left/Right Arrow** - Swipe between responses
+- **Ctrl+Enter** - Send message (alternative)
+- **Up Arrow** - Edit last user message (when input is at start)
+- **Left/Right Arrow** - Navigate between response alternatives
+- **Escape** - Close panels/modals, cancel editing
+- **Ctrl+K** - Focus message input
+- **Ctrl+/** - Toggle Roleplay Tools panel
 
 ## Roadmap