deploy(prod): pre-deploy DB backup + paired code/DB rollback skill

Every `just deploy` now takes a pg_dumpall to
/opt/colectivo/backups/predeploy-<ts>-<sha>.sql.gz BEFORE rebuilding the
app or applying migrations, aborts the deploy if the dump is < 1 KiB,
and (on success) appends `<iso-ts> \t <sha> \t <backup-file>` to
/opt/colectivo/.deploys.log on ambrosio. Keeps the newest 10 backups
(prunes older predeploy-* files).

New `infra/scripts/rollback-erosi.sh` reads .deploys.log and pairs a
code rollback with a DB restore atomically:

  just rollback-list          # show recent deploys
  just rollback               # roll back to N-1
  just rollback-to <sha>      # roll back to a specific deploy
  just rollback-code          # roll back code only, keep current DB

Rollback safety:
- 5-second abort window.
- Verifies the target SHA exists locally + the backup is still on prod
  (warns if it's been pruned past the 10-deploy window).
- Uses a temporary git worktree so the user's working tree isn't
  disturbed.
- Stops app/auth/rest/realtime/storage before the gunzip|psql restore.
- Rebuilds the app image at the rolled-back SHA with the same GIT_SHA
  build-arg path the deploy uses (so __APP_COMMIT__ in the bundle
  matches the running code).
- Does NOT write a new .deploys.log entry — rollback is intentionally
  not a deploy event; the next `just deploy` is from current HEAD.
- Storage volume (/var/lib/storage user uploads) is NOT rolled back.

Justfile `deploy` recipe repointed from the stale `deploy.sh` (which
referenced GHCR pull) to `deploy-erosi.sh` (the active prod path).

New project-scoped skill: `.claude/skills/deploy/SKILL.md` documents the
flow + safety boundaries for Claude-assisted invocations. `.gitignore`
keeps `.claude/settings.local.json` ignored but tracks `.claude/skills/`.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.gitignore

@@ -42,6 +42,9 @@ apps/web/tests/.auth/
 # PWA dev-mode service worker output
 apps/web/dev-dist/
 
-# Claude Code per-project runtime state (schedulers etc.)
-.claude/
+# Claude Code per-project runtime state (schedulers etc.). Project-scoped
+# skills under .claude/skills/ ARE tracked — they document workflows for
+# anyone working on the repo.
+.claude/*
+!.claude/skills/
 graphify-out/cache/