Feature Request: Auto-Save Conversations

# Feature Request: Auto-Save Conversations

## Summary
Add automatic conversation saving functionality to Q CLI, allowing users to enable auto-saving of conversations without manually using the `/save` command.

## Motivation
Currently, users must manually execute `/save ` to preserve their conversations. This can lead to data loss if users forget to save important conversations or if the CLI crashes unexpectedly. An auto-save feature would provide:

- **Data Protection**: Automatic preservation of conversation history
- **User Convenience**: No need to remember to manually save
- **Workflow Continuity**: Seamless conversation preservation during long sessions

## Proposed Solution

### Settings
Add two new configuration settings:
- `chat.enableAutoSave` (boolean, default: `false`) - Enable/disable auto-save functionality
- `chat.autoSavePath` (string, default: `"auto-save-{timestamp}.json"`) - File path pattern for auto-saved conversations

### Behavior
- **Trigger**: Auto-save after each AI response completion
- **File Naming**: Generate filename at session start (e.g., `auto-save-20241030-143915.json`)
- **File Management**: Overwrite the same file throughout the session
- **Error Handling**: Log errors quietly without interrupting the conversation
- **User Experience**: Silent operation (no notifications)

### Usage Example
```bash
# Enable auto-save
q settings chat.enableAutoSave true

# Start conversation - auto-save file created at session start
q chat

# Each AI response automatically saves to the session file
# No manual intervention required
```

## Implementation Plan

### Minimal Changes Required (~15 lines)
1. **Settings Addition** (3 lines in `settings.rs`)
- Add `ChatEnableAutoSave` and `ChatAutoSavePath` to Setting enum
- Add corresponding string mappings

2. **Auto-Save Logic** (8-10 lines)
- Check if auto-save is enabled
- Generate session filename on first save
- Reuse existing persist logic from `/save` command
- Handle errors gracefully with logging

3. **Integration Point** (2-3 lines)
- Call auto-save function after AI response completion
- Integrate with existing conversation state management

### Files to Modify
- `crates/chat-cli/src/database/settings.rs` - Add new settings
- `crates/chat-cli/src/cli/chat/mod.rs` - Add auto-save call
- `crates/chat-cli/src/cli/chat/cli/persist.rs` - Extract reusable save logic (optional)

## Alternatives Considered
1. **Auto-save on user input**: Less intuitive, doesn't capture complete conversation turns
2. **Interval-based saving**: More complex, less predictable behavior
3. **Always-on auto-save**: Could surprise users, violates principle of least surprise

## Compatibility
- **Backward Compatible**: Feature is opt-in (disabled by default)
- **No Breaking Changes**: Existing `/save` and `/load` functionality unchanged
- **File Format**: Uses same JSON format as manual `/save`

## Testing Strategy
- Unit tests for auto-save logic
- Integration tests for setting management
- Error handling tests (disk full, permission denied)
- User workflow tests (enable/disable, file creation)

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This feature addresses a common user need while maintaining Q CLI's existing behavior and design principles. The implementation is minimal and non-intrusive, making it a low-risk addition with high user value.