deploy: Dockerfile + Google Cloud Run recipe

Add a CGO-free static Dockerfile (distroless) and a one-shot Cloud Run
deploy recipe (deploy/gcp-cloudrun.sh + README): single-instance hub on
Cloud Run, metadata in Cloud SQL Postgres (the new `database` backend),
blobs/journals in a GCS bucket, config + DB password in Secret Manager,
least-privilege runtime service account.

Pinned to max-instances=1 (the current build assumes one writer). Verified
end to end against a live deployment.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01R7Q9ZKSZRTdvrSJkYLUmYs

.dockerignore

@@ -0,0 +1,10 @@
+.git
+bdrive
+deploy
+example
+website
+*.md
+.goreleaser.yaml
+.claude
+plugin
+/private