feat: add project reset functionality with quick and full reset options

Add the ability to reset a project to its initial state with two options:
- Quick Reset: Clears features.db, assistant.db, and settings files while
  preserving app spec and prompts
- Full Reset: Deletes everything including prompts directory, triggering
  the setup wizard for project reconfiguration

Backend changes:
- Add POST /{name}/reset endpoint to projects router with full_reset query param
- Validate agent lock file to prevent reset while agent is running (409 Conflict)
- Dispose database engines before deleting files to release Windows file locks
- Add engine caching to api/database.py for better connection management
- Add dispose_engine() functions to both database modules
- Delete WAL mode journal files (*.db-wal, *.db-shm) during reset

Frontend changes:
- Add ResetProjectModal component with toggle between Quick/Full reset modes
- Add ProjectSetupRequired component shown when has_spec is false
- Add resetProject API function and useResetProject React Query hook
- Integrate reset button in header (disabled when agent running)
- Add 'R' keyboard shortcut to open reset modal
- Show ProjectSetupRequired when project needs setup after full reset

This implements the feature from PR #4 directly on master to avoid merge
conflicts.

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

server/routers/projects.py

@@ -373,6 +373,87 @@ async def get_project_stats_endpoint(name: str):
     return get_project_stats(project_dir)
 
 
+@router.post("/{name}/reset")
+async def reset_project(name: str, full_reset: bool = False):
+    """
+    Reset a project to its initial state.
+
+    Args:
+        name: Project name to reset
+        full_reset: If True, also delete prompts/ directory (triggers setup wizard)
+
+    Returns:
+        Dictionary with list of deleted files and reset type
+    """
+    _init_imports()
+    (_, _, get_project_path, _, _, _, _) = _get_registry_functions()
+
+    name = validate_project_name(name)
+    project_dir = get_project_path(name)
+
+    if not project_dir:
+        raise HTTPException(status_code=404, detail=f"Project '{name}' not found")
+
+    if not project_dir.exists():
+        raise HTTPException(status_code=404, detail="Project directory not found")
+
+    # Check if agent is running
+    lock_file = project_dir / ".agent.lock"
+    if lock_file.exists():
+        raise HTTPException(
+            status_code=409,
+            detail="Cannot reset project while agent is running. Stop the agent first."
+        )
+
+    # Dispose of database engines to release file locks (required on Windows)
+    # Import here to avoid circular imports
+    from api.database import dispose_engine as dispose_features_engine
+    from server.services.assistant_database import dispose_engine as dispose_assistant_engine
+
+    dispose_features_engine(project_dir)
+    dispose_assistant_engine(project_dir)
+
+    deleted_files: list[str] = []
+
+    # Files to delete in quick reset
+    quick_reset_files = [
+        "features.db",
+        "features.db-wal",  # WAL mode journal file
+        "features.db-shm",  # WAL mode shared memory file
+        "assistant.db",
+        "assistant.db-wal",
+        "assistant.db-shm",
+        ".claude_settings.json",
+        ".claude_assistant_settings.json",
+    ]
+
+    for filename in quick_reset_files:
+        file_path = project_dir / filename
+        if file_path.exists():
+            try:
+                file_path.unlink()
+                deleted_files.append(filename)
+            except Exception as e:
+                raise HTTPException(status_code=500, detail=f"Failed to delete {filename}: {e}")
+
+    # Full reset: also delete prompts directory
+    if full_reset:
+        prompts_dir = project_dir / "prompts"
+        if prompts_dir.exists():
+            try:
+                shutil.rmtree(prompts_dir)
+                deleted_files.append("prompts/")
+            except Exception as e:
+                raise HTTPException(status_code=500, detail=f"Failed to delete prompts/: {e}")
+
+    return {
+        "success": True,
+        "reset_type": "full" if full_reset else "quick",
+        "deleted_files": deleted_files,
+        "message": f"Project '{name}' has been reset" + (" (full reset)" if full_reset else " (quick reset)")
+    }
+
+
 @router.patch("/{name}/settings", response_model=ProjectDetail)
 async def update_project_settings(name: str, settings: ProjectSettingsUpdate):
     """Update project-level settings (concurrency, etc.)."""

server/services/assistant_database.py

@@ -79,6 +79,26 @@ def get_engine(project_dir: Path):
     return _engine_cache[cache_key]
 
 
+def dispose_engine(project_dir: Path) -> bool:
+    """Dispose of and remove the cached engine for a project.
+
+    This closes all database connections, releasing file locks on Windows.
+    Should be called before deleting the database file.
+
+    Returns:
+        True if an engine was disposed, False if no engine was cached.
+    """
+    cache_key = project_dir.as_posix()
+
+    if cache_key in _engine_cache:
+        engine = _engine_cache.pop(cache_key)
+        engine.dispose()
+        logger.debug(f"Disposed database engine for {cache_key}")
+        return True
+
+    return False
+
+
 def get_session(project_dir: Path):
     """Get a new database session for a project."""
     engine = get_engine(project_dir)