gateway: deploy config.yaml changes (the volume was shadowing the image)

Deploying the audio-pricing change proved the gap: the image built and the app
restarted, but /model/info still served the old prices — /app/data is a
persistent volume, so the Dockerfile's COPY config.yaml /app/data/config.yaml is
shadowed by the volume's file from the first install, and start.sh only wrote a
default when the file was missing. Config changes in this repo therefore never
reached a running gateway; the audit's byte-identical md5 check was a manual
sync.

Fix: ship a second copy at /app/code/config.yaml and have start.sh sync it over
the volume at boot whenever they differ. The repo stays the source of truth, the
legacy first-boot default remains, and the README documents the flow.

Dockerfile

@@ -19,6 +19,9 @@ RUN chmod +x /app/code/start.sh
 
 # Default config — will be overridden by Cloudron env vars at runtime
 COPY config.yaml /app/data/config.yaml
+# A second copy inside the image: start.sh syncs it over the persistent
+# /app/data volume at boot, so config changes in the repo actually deploy.
+COPY config.yaml /app/code/config.yaml
 
 # Append the co-op credit-pack hint to LiteLLM's hardcoded budget-exceeded
 # messages. Done at BUILD time — the runtime rootfs is read-only under