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.

litellm_config.yaml

@@ -25,6 +25,7 @@ environment_variables:
   NOVITA_API_KEY: os.environ/NOVITA_API_KEY
   GROQ_API_KEY: os.environ/GROQ_API_KEY
   GEMINI_API_KEY: os.environ/GEMINI_API_KEY
+  GIGACHAT_CREDENTIALS: os.environ/GIGACHAT_CREDENTIALS
 
 router_settings:
   routing_strategy: simple-shuffle
@@ -43,6 +44,15 @@ router_settings:
   default_fallbacks: ["a-medium-code", "a-complex", "groq-qwen-coder"]
 
 model_list:
+  # --- LLM tier classifier (GigaChat freemium, hybrid mode only) ---
+  - model_name: gigachat-classifier
+    litellm_params:
+      model: gigachat/GigaChat-2-Lite
+      api_key: os.environ/GIGACHAT_CREDENTIALS
+      ssl_verify: false
+      max_tokens: 64
+      temperature: 0
+
   # --- Lane models (generated from config/model_matrix.yaml) ---
   - model_name: a-simple
     litellm_params: