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

.github/workflows/ci.yml

@@ -125,5 +125,21 @@ jobs:
           push: false
           provenance: false
           tags: crumbs:ci
+          load: true
           cache-from: type=gha,scope=ci-docker
           cache-to: type=gha,scope=ci-docker,mode=max
+
+      # Regression for #93: a host folder bind-mounted at /data is owned by the
+      # host user (the runner, uid 1001), not the container's node user (1000)
+      - name: Start with a host-owned bind mount
+        run: |
+          mkdir -p "$RUNNER_TEMP/crumbs-data"
+          docker run -d --name crumbs -p 3000:3000 -v "$RUNNER_TEMP/crumbs-data:/data" crumbs:ci
+          for i in $(seq 1 30); do
+            if curl -fsS -o /dev/null http://localhost:3000/login; then
+              test -f "$RUNNER_TEMP/crumbs-data/crumbs.db" && exit 0
+            fi
+            sleep 1
+          done
+          docker logs crumbs
+          exit 1