Rewrite CI/CD pipeline with deploy-tag change detection and verified deployments

Replace HEAD~1 diff with git tag-based change detection to catch all changes
since last successful deploy. Split into 4 parallel jobs: detect, frontend,
API (with migrations, health check, and rollback), and deploy tagging.

api/server.js

@@ -1,7 +1,6 @@
 const express = require('express');
 const { Pool } = require('pg');
 const cors = require('cors');
-// API v1.1 - sales, customers, analytics
 const bcrypt = require('bcryptjs');
 const jwt = require('jsonwebtoken');
 require('dotenv').config();