feat(api): add log_request_body_enabled feature flag support

Add runtime feature flag to control whether request bodies are stored
in logs. The Handler now accepts a Redis client to check the
log_request_body_enabled feature flag before persisting log records.

- Add logRequestBodyFeatureKey constant for feature flag
- Inject Redis client into Handler for feature flag lookups
- Strip request body from log records when feature is disabled
- Update tests to pass Redis client to NewHandler

internal/api/model_handler_test.go

@@ -33,7 +33,7 @@ func newTestHandlerWithRedis(t *testing.T) (*Handler, *gorm.DB, *miniredis.Minir
 	mr := miniredis.RunT(t)
 	rdb := redis.NewClient(&redis.Options{Addr: mr.Addr()})
 	sync := service.NewSyncService(rdb)
-	return NewHandler(db, sync, nil), db, mr
+	return NewHandler(db, sync, nil, rdb), db, mr
 }
 
 func TestCreateModel_DefaultsKindChat_AndWritesModelsMeta(t *testing.T) {