Add connection review page with optional message on connection requests

- New GET route and template for reviewing individual connection requests
- Optional personal message field when sending connection requests
- Message visible to recipient on review page and connection list
- Dashboard "Review" button links to per-connection review page
- QR scan flow shows message prompt before sending request
- Fix accepted connections query: include both sent and received
- Fix url_for('uploaded_file') -> url_for('static', 'uploads/')
- Fix request.json -> request.is_json to avoid 415 on form POST
- Remove card from DOM on approve/reject instead of page reload

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

init_db.py

@@ -257,6 +257,7 @@ def create_tables():
         "ALTER TABLE staff ADD COLUMN reminder_count INT DEFAULT 0",
         "ALTER TABLE staff ADD COLUMN reminder_dates JSON DEFAULT NULL",
         "ALTER TABLE breakout_session_organizers ADD COLUMN presenter_code VARCHAR(10) UNIQUE DEFAULT NULL",
+        "ALTER TABLE connections ADD COLUMN message TEXT DEFAULT NULL",
     ]
 
     try: