Phase 2: Add reasoning and TipTap content endpoints

- Extend Document model with reasoning_type, confidence, reasoning_steps, model_source, tiptap_content fields
- Add new endpoints:
  - GET /documents/{id}/reasoning - Get reasoning metadata
  - PATCH /documents/{id}/reasoning - Update reasoning metadata
  - GET /documents/{id}/reasoning-panel - Get reasoning panel data for UI
  - POST /documents/{id}/reasoning-steps - Add reasoning step
  - DELETE /documents/{id}/reasoning-steps/{step} - Delete reasoning step
  - GET /documents/{id}/content?format=tiptap|markdown - Get content in TipTap or Markdown
  - PUT /documents/{id}/content - Update content (supports both TipTap JSON and Markdown)
- Add TipTap to Markdown conversion
- Update database schema with new columns
- Add comprehensive tests for all new endpoints
- All 37 tests passing

app/database.py

@@ -185,7 +185,12 @@ def _create_schema(sync_conn):
             deleted_at TIMESTAMP NULL,
             deleted_by TEXT NULL,
             created_at TIMESTAMP NOT NULL DEFAULT (datetime('now')),
-            updated_at TIMESTAMP NOT NULL DEFAULT (datetime('now'))
+            updated_at TIMESTAMP NOT NULL DEFAULT (datetime('now')),
+            reasoning_type TEXT,
+            confidence TEXT,
+            reasoning_steps TEXT,
+            model_source TEXT,
+            tiptap_content TEXT
         )
     """))