Fix Docker runtime errors: migrate to google-genai SDK and fix SQLite permissions

Migrate from deprecated google-generativeai to google-genai (>=1.0) using the
new Client-based API, and fix SQLite "unable to open database file" in Docker
by chowning the data directory to appuser before switching users.

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

Dockerfile

@@ -35,6 +35,7 @@ RUN mkdir -p data
 
 # Non-root user
 RUN useradd --create-home appuser
+RUN chown appuser:appuser data
 USER appuser
 
 HEALTHCHECK --interval=30s --timeout=5s --retries=3 \