feat: add Azure OpenAI / MS Foundry support for /api/ask

- Add LLM_API_VERSION config for Azure api-version query param
- Detect Azure endpoints and use api-key header instead of Bearer
- Handle base URLs that already include /chat/completions path
- Update .env.example with Azure OpenAI guidance

backend/config.py

@@ -48,6 +48,7 @@ class Settings(BaseSettings):
     LLM_MODEL: str = "gpt-4o-mini"
     LLM_MAX_EVENTS: int = 50
     LLM_TIMEOUT_SECONDS: int = 30
+    LLM_API_VERSION: str = ""  # e.g. 2025-01-01-preview for Azure OpenAI
 
 
 _settings = Settings()
@@ -81,3 +82,4 @@ LLM_BASE_URL = _settings.LLM_BASE_URL
 LLM_MODEL = _settings.LLM_MODEL
 LLM_MAX_EVENTS = _settings.LLM_MAX_EVENTS
 LLM_TIMEOUT_SECONDS = _settings.LLM_TIMEOUT_SECONDS
+LLM_API_VERSION = _settings.LLM_API_VERSION