feat: add admin endpoint to send digest emails for users

- Implemented a new endpoint `/admin/test/send-digest` in `admin_api.py` to trigger digest emails for specific users.
- Added a script `send_digest.py` to facilitate sending digest emails via the admin API.
- Enhanced the digest action handling in `digest_action_api.py` to support token peeking without consuming it.
- Updated the `send_digests` function in `digest_scheduler.py` to utilize the new `send_digest_for_user` function for sending emails.
- Introduced a new utility function `peek_token` in `digest_token.py` to validate tokens without consuming them.
- Modified the `ParentView.vue` component to handle digest actions upon receiving a digest token in the URL.
- Updated `.gitignore` to exclude sensitive certificate files.

backend/api/admin_api.py

@@ -206,3 +206,44 @@ def create_test_digest_token():
         return jsonify({'token': token.id}), 200
     except Exception as e:
         return jsonify({'error': str(e), 'code': 'SERVER_ERROR'}), 500
+
+
+@admin_api.route('/admin/test/send-digest', methods=['POST'])
+def send_test_digest():
+    """Trigger a digest email for a specific user by email address.
+
+    Only active when DB_ENV is not 'production'. Requires admin authentication.
+    Note: actual email delivery is skipped in e2e mode by email_sender.
+    """
+    if os.environ.get('DB_ENV') == 'production':
+        return jsonify({'error': 'Not found', 'code': 'NOT_FOUND'}), 404
+
+    user_id = get_validated_user_id()
+    if not user_id:
+        return jsonify({'error': 'Unauthorized', 'code': 'UNAUTHORIZED'}), 401
+
+    # Verify caller is admin
+    caller_dict = users_db.get(Query().id == user_id)
+    if not caller_dict or caller_dict.get('role') != 'admin':
+        return jsonify({'error': 'Admin access required', 'code': 'ADMIN_REQUIRED'}), 403
+
+    data = request.get_json() or {}
+    email = data.get('email', '').strip().lower()
+    if not email:
+        return jsonify({'error': 'email is required', 'code': 'MISSING_FIELDS'}), 400
+
+    target = users_db.get(Query().email == email)
+    if not target:
+        return jsonify({'error': 'User not found', 'code': 'USER_NOT_FOUND'}), 404
+
+    target_id = target.get('id')
+    target_email = target.get('email')
+
+    try:
+        from flask import current_app
+        from utils.digest_scheduler import send_digest_for_user
+        frontend_url = current_app.config.get('FRONTEND_URL', 'https://localhost:5173')
+        items_sent = send_digest_for_user(target_id, target_email, frontend_url)
+        return jsonify({'items_sent': items_sent}), 200
+    except Exception as e:
+        return jsonify({'error': str(e), 'code': 'SERVER_ERROR'}), 500