chore: relocate backend into apps/api ahead of monorepo merge

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/api/README.md

@@ -0,0 +1,18 @@
+# STAR Phase 1 — Tier 1 Auth System
+## Technical Documentation
+
+**Version:** 1.0.0  
+**Date:** October 6, 2025  
+**Stack:** Node.js · Express · Sequelize (PostgreSQL) · JWT · Google OAuth 2.0 · Nodemailer
+**Deployment** DigitalOcean Droplet (3 Droplets for API + S3 and Postgres)
+
+## TODO
+Branchings and Tags (Backups)
+```
+main (protected)     → prod
+qas (protected)      → staging
+dev (protected*)     → integration/playground
+feature/xyz           → short-lived, deleted after merge
+hotfix/xyz             → for urgent prod patches
++ tags (v1.0.9...)    → released snapshots
+```