feature: trips
GET /api/trips/by-user ✅
GET /api/trips/by-trip/{trip_id} ✅
GET /api/trips/{trip_id}/summarize ✅
GET /api/trips/recommended ✅
GET /api/trips/invited ✅
POST /api/trips ✅
PATCH /api/trips/{trip_id} ✅
DELETE /api/trips/{trip_id} ✅
DELETE /api/trips/{trip_id}/leave ✅