Add in-progress status tracking for features

Implements feature locking to prevent multiple agent sessions from working
on the same feature simultaneously. This is essential for parallel agent
execution.

Database changes:
- Add `in_progress` boolean column to Feature model
- Add migration function to handle existing databases

MCP Server tools:
- Add `feature_mark_in_progress` - lock feature when starting work
- Add `feature_clear_in_progress` - unlock feature when abandoning
- Update `feature_get_next` to skip in-progress features
- Update `feature_get_stats` to include in_progress count
- Update `feature_mark_passing` and `feature_skip` to clear in_progress

Backend updates:
- Update progress.py to track and display in_progress count
- Update features router to properly categorize in-progress features
- Update WebSocket to broadcast in_progress in progress updates
- Add in_progress to FeatureResponse schema

Frontend updates:
- Add in_progress to TypeScript types (Feature, ProjectStats, WSProgressMessage)
- Update useWebSocket hook to track in_progress state

Prompt template:
- Add instructions for agents to mark features in-progress immediately
- Document new MCP tools in allowed tools section

Also fixes spec_chat_session.py to use absolute project path instead of
relative path for consistency with CLI behavior.

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

server/routers/projects.py

@@ -73,7 +73,7 @@ def validate_project_name(name: str) -> str:
 def get_project_stats(project_dir: Path) -> ProjectStats:
     """Get statistics for a project."""
     _init_imports()
-    passing, total = _count_passing_tests(project_dir)
+    passing, _, total = _count_passing_tests(project_dir)
     percentage = (passing / total * 100) if total > 0 else 0.0
     return ProjectStats(passing=passing, total=total, percentage=round(percentage, 1))