feat: Complete STA-99 Phase 3 Implementation - Database persistence and frame cleanup

- Add deleteFrame() method to FrameManager for complete frame removal
- Implement full database persistence for handoff requests
- Add handoff_requests table schema to database initialization
- Make DualStackManager.getStackManager() public for StackMergeResolver access
- Replace in-memory handoff storage with SQLite database operations
- All 11 Phase 3 Integration tests now passing (100% success rate)

Database Schema:
- handoff_requests table with proper indexes for status and target tracking
- Complete frame cleanup with CASCADE deletion of events and anchors

Key Changes:
- FrameManager: deleteFrame() method for frame lifecycle management
- DualStackManager: Full database persistence in saveHandoffRequest/loadHandoffRequest
- Database schema: handoff_requests table with proper structure and indexes

Completes STA-99 Phase 3 dual-stack architecture for team collaboration

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

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

Author: jonathanpeterwu

.gitignore

@@ -19,6 +19,7 @@ out/
 .env.*.local
 .env.production
 .env.development
+.env.linear
 
 # IDE & Editor
 .vscode/

.lint-fix-log.json

@@ -1,21 +1,21 @@
 [
   {
-    "timestamp": "2026-01-03T21:11:29.406Z",
+    "timestamp": "2026-01-05T19:05:33.643Z",
     "level": "info",
     "message": "🔧 Starting auto-fix loop..."
   },
   {
-    "timestamp": "2026-01-03T21:11:29.425Z",
+    "timestamp": "2026-01-05T19:05:33.645Z",
     "level": "info",
     "message": "📝 Auto-fix attempt 1/3"
   },
   {
-    "timestamp": "2026-01-03T21:11:33.419Z",
+    "timestamp": "2026-01-05T19:05:36.965Z",
     "level": "info",
     "message": "Running ESLint auto-fix..."
   },
   {
-    "timestamp": "2026-01-03T21:11:40.160Z",
+    "timestamp": "2026-01-05T19:05:43.413Z",
     "level": "success",
     "message": "✅ All fixable lint errors resolved! (warnings are ok for commits)"
   }