feat(config): log resolved llm and embedding model names on startup

Add INFO log in get_settings() to print the actual model names
after merging .env and class defaults. Confirms pydantic-settings
priority: env values override class defaults as expected.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

backend/app/core/config.py

@@ -1,8 +1,11 @@
 from functools import lru_cache
+import logging
 from pathlib import Path
 
 from pydantic_settings import BaseSettings
 
+logger = logging.getLogger(__name__)
+
 
 class Settings(BaseSettings):
     # LLM access
@@ -41,4 +44,6 @@ class Settings(BaseSettings):
 
 @lru_cache
 def get_settings() -> Settings:
-    return Settings()
+    s = Settings()
+    logger.info("Settings loaded: llm_model=%s  embedding_model=%s", s.llm_model_name, s.embedding_model)
+    return s