feat(classifier): optional GigaChat-2-Lite hybrid tier classify

LLM classify via LiteLLM gigachat-classifier when heuristic confidence
is low. CLASSIFIER_MODE=heuristic|hybrid|llm. Metrics classifier_source.

docker-stack.yml

@@ -44,6 +44,8 @@ secrets:
     external: true
   gemini_api_key:
     external: true
+  gigachat_credentials:
+    external: true
   vless_conf:
     external: true
 
@@ -119,6 +121,7 @@ services:
       - postgres_password
       - groq_api_key
       - gemini_api_key
+      - gigachat_credentials
     networks:
       ai-internal:
         aliases:
@@ -162,6 +165,8 @@ services:
       REDIS_URL: redis://redis:6379/0
       CONFIG_DIR: /app/config
       DEFAULT_QUALITY_MODE: ${DEFAULT_QUALITY_MODE:-auto}
+      CLASSIFIER_MODE: ${CLASSIFIER_MODE:-hybrid}
+      CLASSIFIER_LLM_MODEL: ${CLASSIFIER_LLM_MODEL:-gigachat-classifier}
     secrets:
       - litellm_master_key
       - router_api_key