refactor: remove unused OPENAI_API_KEY and GOOGLE_API_KEY

Removed all references to OPENAI_API_KEY and GOOGLE_API_KEY since only
Claude (Anthropic) provider is implemented. These were placeholder references
for future providers that don't exist yet.

Changes:
- Removed OPENAI_API_KEY and GOOGLE_API_KEY from docker-compose.yml
- Removed from .env and .env.example files
- Updated setup/routes/store-api-key.ts to only support anthropic
- Updated setup/routes/delete-api-key.ts to only support anthropic
- Updated setup/routes/api-keys.ts to only return anthropic key status
- Updated models/routes/providers.ts to only list anthropic provider
- Updated auto-mode-service.ts error message to only reference ANTHROPIC_API_KEY

Backend test results: 653/653 passing ✅

🤖 Generated with Claude Code

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

docker-compose.yml

@@ -48,10 +48,6 @@ services:
 
       # Optional - CORS origin (default allows all)
       - CORS_ORIGIN=${CORS_ORIGIN:-*}
-
-      # Optional - additional API keys
-      - OPENAI_API_KEY=${OPENAI_API_KEY:-}
-      - GOOGLE_API_KEY=${GOOGLE_API_KEY:-}
     volumes:
       # ONLY named volumes - these are isolated from your host filesystem
       # This volume persists data between restarts but is container-managed