feat: implement auto-sync scheduler for LoTW and DCL

Add automatic synchronization scheduler that allows users to configure
periodic sync intervals for LoTW and DCL via the settings page.

Features:
- Users can enable/disable auto-sync per service (LoTW/DCL)
- Configurable sync intervals (1-720 hours)
- Settings page UI for managing auto-sync preferences
- Dashboard shows upcoming scheduled auto-sync jobs
- Scheduler runs every minute, triggers syncs when due
- Survives server restarts via database persistence
- Graceful shutdown support (SIGINT/SIGTERM)

Backend:
- New autoSyncSettings table with user preferences
- auto-sync.service.js for CRUD operations and scheduling logic
- scheduler.service.js for periodic tick processing
- API endpoints: GET/PUT /auto-sync/settings, GET /auto-sync/scheduler/status

Frontend:
- Auto-sync settings section in settings page
- Upcoming auto-sync section on dashboard with scheduled job cards
- Purple-themed UI for scheduled jobs with countdown animation

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

src/backend/migrations/add-auto-sync-settings.js

@@ -0,0 +1,111 @@
+/**
+ * Migration: Add auto_sync_settings table
+ *
+ * This script creates the auto_sync_settings table for managing
+ * automatic sync intervals for DCL and LoTW services.
+ * Users can enable/disable auto-sync and configure sync intervals.
+ */
+
+import Database from 'bun:sqlite';
+import { join, dirname } from 'path';
+import { fileURLToPath } from 'url';
+
+// ES module equivalent of __dirname
+const __filename = fileURLToPath(import.meta.url);
+const __dirname = dirname(__filename);
+
+const dbPath = join(__dirname, '../award.db');
+const sqlite = new Database(dbPath);
+
+async function migrate() {
+  console.log('Starting migration: Add auto-sync settings...');
+
+  try {
+    // Check if auto_sync_settings table already exists
+    const tableExists = sqlite.query(`
+      SELECT name FROM sqlite_master
+      WHERE type='table' AND name='auto_sync_settings'
+    `).get();
+
+    if (tableExists) {
+      console.log('Table auto_sync_settings already exists. Skipping...');
+    } else {
+      // Create auto_sync_settings table
+      sqlite.exec(`
+        CREATE TABLE auto_sync_settings (
+          user_id INTEGER PRIMARY KEY,
+          lotw_enabled INTEGER NOT NULL DEFAULT 0,
+          lotw_interval_hours INTEGER NOT NULL DEFAULT 24,
+          lotw_last_sync_at INTEGER,
+          lotw_next_sync_at INTEGER,
+          dcl_enabled INTEGER NOT NULL DEFAULT 0,
+          dcl_interval_hours INTEGER NOT NULL DEFAULT 24,
+          dcl_last_sync_at INTEGER,
+          dcl_next_sync_at INTEGER,
+          created_at INTEGER NOT NULL DEFAULT (strftime('%s', 'now') * 1000),
+          updated_at INTEGER NOT NULL DEFAULT (strftime('%s', 'now') * 1000),
+          FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE
+        )
+      `);
+
+      // Create index for faster queries on next_sync_at
+      sqlite.exec(`
+        CREATE INDEX idx_auto_sync_settings_lotw_next_sync_at
+        ON auto_sync_settings(lotw_next_sync_at)
+        WHERE lotw_enabled = 1
+      `);
+
+      sqlite.exec(`
+        CREATE INDEX idx_auto_sync_settings_dcl_next_sync_at
+        ON auto_sync_settings(dcl_next_sync_at)
+        WHERE dcl_enabled = 1
+      `);
+
+      console.log('Created auto_sync_settings table with indexes');
+    }
+
+    console.log('Migration complete! Auto-sync settings table added to database.');
+  } catch (error) {
+    console.error('Migration failed:', error);
+    sqlite.close();
+    process.exit(1);
+  }
+
+  sqlite.close();
+}
+
+async function rollback() {
+  console.log('Starting rollback: Remove auto-sync settings...');
+
+  try {
+    // Drop indexes first
+    sqlite.exec(`DROP INDEX IF EXISTS idx_auto_sync_settings_lotw_next_sync_at`);
+    sqlite.exec(`DROP INDEX IF EXISTS idx_auto_sync_settings_dcl_next_sync_at`);
+
+    // Drop table
+    sqlite.exec(`DROP TABLE IF EXISTS auto_sync_settings`);
+
+    console.log('Rollback complete! Auto-sync settings table removed from database.');
+  } catch (error) {
+    console.error('Rollback failed:', error);
+    sqlite.close();
+    process.exit(1);
+  }
+
+  sqlite.close();
+}
+
+// Check if this is a rollback
+const args = process.argv.slice(2);
+if (args.includes('--rollback') || args.includes('-r')) {
+  rollback().then(() => {
+    console.log('Rollback script completed successfully');
+    process.exit(0);
+  });
+} else {
+  // Run migration
+  migrate().then(() => {
+    console.log('Migration script completed successfully');
+    process.exit(0);
+  });
+}