fix(showcase): add OCI source labels to pocketbase Dockerfile

GHCR auto-links container packages to their source repository when the
image includes org.opencontainers.image.source. Without this label the
package's repository field stays null on the API, which triggers the
daily drift audit alert even though Actions access is configured.

Author: jpr5

showcase/pocketbase/Dockerfile

@@ -33,6 +33,8 @@ RUN set -eux; \
     /pb/pocketbase --version
 
 FROM alpine:3.19
+LABEL org.opencontainers.image.source="https://github.com/CopilotKit/CopilotKit"
+LABEL org.opencontainers.image.description="PocketBase for CopilotKit showcase platform"
 # `su-exec` is alpine's minimal privilege-drop helper (~30 KB static
 # binary). Used by entrypoint.sh to run PocketBase as `pocketbase` while
 # still being able to chown /pb_data at container start — see the