fix(ai): stabilize GCP Ollama alert lane

apps/api/src/core/config.py

@@ -520,6 +520,14 @@ class Settings(BaseSettings):
             "then local 111 before cloud backup providers such as Gemini."
         ),
     )
+    ALERT_OLLAMA_MODEL: str = Field(
+        default="gemma3:4b",
+        description=(
+            "Ollama model used for incident/alert diagnosis. Keep this separate "
+            "from the general RCA model so alert cards stay on the fast local "
+            "lane before Gemini backup is considered."
+        ),
+    )
     # 2026-03-29 ogt: ADR-036 Nemotron Tool Calling 整合
     NVIDIA_API_KEY: str = Field(
         default="",