Refactor monolithic modules and harden booking, email, and auth infrastructure.

Split oversized frontend API client, email service, and admin/booking pages into focused modules while preserving import surfaces, and add Redis-backed queues, stale booking cleanup, stronger auth, and scale deployment configs.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/src/db/migrate.ts

@@ -432,6 +432,18 @@ async function migrate() {
       )
     `);
 
+    await (db as any).run(sql`
+      CREATE TABLE IF NOT EXISTS email_queue (
+        id TEXT PRIMARY KEY,
+        params TEXT NOT NULL,
+        status TEXT NOT NULL DEFAULT 'pending',
+        attempts INTEGER NOT NULL DEFAULT 0,
+        last_error TEXT,
+        created_at TEXT NOT NULL,
+        processed_at TEXT
+      )
+    `);
+
     // Site settings table
     await (db as any).run(sql`
       CREATE TABLE IF NOT EXISTS site_settings (
@@ -899,6 +911,18 @@ async function migrate() {
       )
     `);
 
+    await (db as any).execute(sql`
+      CREATE TABLE IF NOT EXISTS email_queue (
+        id UUID PRIMARY KEY,
+        params TEXT NOT NULL,
+        status VARCHAR(20) NOT NULL DEFAULT 'pending',
+        attempts INTEGER NOT NULL DEFAULT 0,
+        last_error TEXT,
+        created_at TIMESTAMP NOT NULL,
+        processed_at TIMESTAMP
+      )
+    `);
+
     // Site settings table
     await (db as any).execute(sql`
       CREATE TABLE IF NOT EXISTS site_settings (