fix(docker): make bind-mounted data folders writable on startup

The image switched to the node user (uid 1000) at build time, so a host
folder mounted at /data kept its host ownership and SQLite failed with
SQLITE_CANTOPEN in a restart loop. Named and anonymous volumes worked only
because Docker copies the image's /data ownership into them.

The container now starts as root, hands DATA_DIR and the database folder
to node (only entries not already owned by it), and execs the app via
setpriv as node. Containers started with an explicit `user:` skip this.

Adds a CI step that runs the image with a host-owned bind mount.

Fixes #93

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016MHECwBhBpM248EFSBi4L5

Dockerfile

@@ -37,8 +37,10 @@ COPY --from=build /app/package.json ./
 # Create data directory
 RUN mkdir -p /data && chown -R node:node /data
 
-# Use non-root user
-USER node
+# Runs as root only long enough to hand the data folder (often a host bind
+# mount) to the node user, then drops privileges — see crumbs-entrypoint.sh
+COPY crumbs-entrypoint.sh /usr/local/bin/crumbs-entrypoint.sh
+ENTRYPOINT ["crumbs-entrypoint.sh"]
 
 # Configuration
 ENV NODE_ENV=production