Email queue + async sending; legal settings and placeholders

- Add in-memory email queue with rate limiting (MAX_EMAILS_PER_HOUR)
- Bulk send to event attendees now queues and returns immediately
- Frontend shows 'Emails are being sent in the background'
- Legal pages, settings, and placeholders updates

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

backend/src/db/migrate.ts

@@ -437,6 +437,25 @@ async function migrate() {
         updated_at TEXT NOT NULL
       )
     `);
+
+    // Legal settings table for legal page placeholder values
+    await (db as any).run(sql`
+      CREATE TABLE IF NOT EXISTS legal_settings (
+        id TEXT PRIMARY KEY,
+        company_name TEXT,
+        legal_entity_name TEXT,
+        ruc_number TEXT,
+        company_address TEXT,
+        company_city TEXT,
+        company_country TEXT,
+        support_email TEXT,
+        legal_email TEXT,
+        governing_law TEXT,
+        jurisdiction_city TEXT,
+        updated_at TEXT NOT NULL,
+        updated_by TEXT REFERENCES users(id)
+      )
+    `);
   } else {
     // PostgreSQL migrations
     await (db as any).execute(sql`
@@ -822,6 +841,25 @@ async function migrate() {
         updated_at TIMESTAMP NOT NULL
       )
     `);
+
+    // Legal settings table for legal page placeholder values
+    await (db as any).execute(sql`
+      CREATE TABLE IF NOT EXISTS legal_settings (
+        id UUID PRIMARY KEY,
+        company_name VARCHAR(255),
+        legal_entity_name VARCHAR(255),
+        ruc_number VARCHAR(50),
+        company_address TEXT,
+        company_city VARCHAR(100),
+        company_country VARCHAR(100),
+        support_email VARCHAR(255),
+        legal_email VARCHAR(255),
+        governing_law VARCHAR(255),
+        jurisdiction_city VARCHAR(100),
+        updated_at TIMESTAMP NOT NULL,
+        updated_by UUID REFERENCES users(id)
+      )
+    `);
   }
 
   console.log('Migrations completed successfully!');