general cleanup - removed old comments, enforced naming conventions etc

backend/infra/migrations/005_create_users_table.sql

@@ -0,0 +1,13 @@
+-- Migration 005: Create users table with UUID primary key
+-- This establishes a local user record for each Firebase-authenticated user.
+
+CREATE TABLE IF NOT EXISTS users (
+  id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+  firebase_uid VARCHAR(128) NOT NULL UNIQUE,
+  email VARCHAR(255) NOT NULL,
+  display_name VARCHAR(255),
+  created_at TIMESTAMP DEFAULT NOW(),
+  updated_at TIMESTAMP DEFAULT NOW()
+);
+
+CREATE INDEX IF NOT EXISTS idx_users_firebase_uid ON users(firebase_uid);