Story 18: Token-by-token streaming responses

- Backend: Added OllamaProvider::chat_stream() with newline-delimited JSON parsing
- Backend: Emit chat:token events for each token received from Ollama
- Backend: Added futures dependency and stream feature for reqwest
- Frontend: Added streamingContent state and chat:token event listener
- Frontend: Real-time token display with auto-scroll
- Frontend: Markdown and syntax highlighting support for streaming content
- Fixed all TypeScript errors (tsc --noEmit)
- Fixed all Biome warnings and errors
- Fixed all Clippy warnings
- Added comprehensive code quality documentation
- Added tsc --noEmit to verification checklist

Tested and verified:
- Tokens stream in real-time
- Auto-scroll works during streaming
- Tool calls interrupt streaming correctly
- Multi-turn conversations work
- Smooth performance with no lag

.living_spec/stories/20_start_new_session.md

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+# Story 20: Start New Session / Clear Chat History
+
+## User Story
+As a user, I want to be able to start a fresh conversation without restarting the entire application, so that I can begin a new task with clean context while keeping the same project open.
+
+## Acceptance Criteria
+- [ ] There is a visible "New Session" or "Clear Chat" button in the UI
+- [ ] Clicking the button clears all messages from the chat history
+- [ ] The input field remains enabled and ready for a new message
+- [ ] The button asks for confirmation before clearing (to prevent accidental data loss)
+- [ ] After clearing, the chat shows an empty state or welcome message
+- [ ] The project path and model settings are preserved (only messages are cleared)
+- [ ] Any ongoing streaming or tool execution is cancelled before clearing
+- [ ] The action is immediate and provides visual feedback
+
+## Out of Scope
+- Saving/exporting previous sessions before clearing
+- Multiple concurrent chat sessions or tabs
+- Undo functionality after clearing
+- Automatic session management or limits
+- Session history or recovery
+
+## Technical Notes
+- Frontend state (`messages`) needs to be cleared
+- Backend may need to be notified to cancel any in-flight operations
+- Should integrate with the cancellation mechanism from Story 13 (if implemented)
+- Button should be placed in the header area near the model selector
+- Consider using a modal dialog for confirmation
+- State: `setMessages([])` to clear the array
+
+## Design Considerations
+- Button placement: Header area (top right or near model controls)
+- Button style: Secondary/subtle to avoid accidental clicks
+- Confirmation dialog: "Are you sure? This will clear all messages."
+- Icon suggestion: 🔄 or "New" text label