Fix deploy.sh skipping SPA build on same-ref/aborted deploys

The build was gated on `git diff BEFORE AFTER`, where BEFORE was HEAD
before checkout. Re-deploying the same ref (or re-running after an
aborted deploy) made BEFORE == AFTER, so the diff was empty and the SPA
build silently skipped — shipping stale assets while migrations still ran.

- Always rebuild the SPA; only gate the heavy dep installs.
- npm ci / composer install also run when node_modules / vendor are missing.
- Track the last successfully deployed commit in .deploy-last-commit and
  diff against that, so an aborted run never advances the baseline.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitignore

@@ -24,4 +24,5 @@ yarn-error.log
 /.zed
 /.tmp/
 /.worktrees/
+/.deploy-last-commit
 /ONSPD_Online_Latest_Centroids_*.csv