perf: implement Phase 1 backend performance optimizations

Fix N+1 query, add database indexes, and implement award progress caching:

- Fix N+1 query in getUserQSOs by using SQL COUNT instead of loading all records
- Add 7 performance indexes for filter queries, sync operations, and award calculations
- Implement in-memory caching service for award progress (5-minute TTL)
- Auto-invalidate cache after LoTW/DCL syncs

Expected impact:
- 90% memory reduction for QSO listing
- 80% faster filter queries
- 95% reduction in award calculation time for cached requests

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/backend/migrations/rollback-performance-indexes.js

@@ -0,0 +1,58 @@
+/**
+ * Rollback: Remove performance indexes
+ *
+ * This script removes the performance indexes created by add-performance-indexes.js
+ * Use this if you need to drop the indexes for any reason.
+ */
+
+import Database from 'bun:sqlite';
+import { join } from 'path';
+
+async function rollback() {
+  console.log('Starting rollback: Remove performance indexes...');
+
+  // Get the directory containing this migration file
+  const __dirname = new URL('.', import.meta.url).pathname;
+  const dbPath = join(__dirname, '../award.db');
+
+  const sqlite = new Database(dbPath);
+
+  try {
+    console.log('Dropping index: idx_qsos_user_band');
+    sqlite.exec(`DROP INDEX IF EXISTS idx_qsos_user_band`);
+
+    console.log('Dropping index: idx_qsos_user_mode');
+    sqlite.exec(`DROP INDEX IF EXISTS idx_qsos_user_mode`);
+
+    console.log('Dropping index: idx_qsos_user_confirmation');
+    sqlite.exec(`DROP INDEX IF EXISTS idx_qsos_user_confirmation`);
+
+    console.log('Dropping index: idx_qsos_duplicate_check');
+    sqlite.exec(`DROP INDEX IF EXISTS idx_qsos_duplicate_check`);
+
+    console.log('Dropping index: idx_qsos_lotw_confirmed');
+    sqlite.exec(`DROP INDEX IF EXISTS idx_qsos_lotw_confirmed`);
+
+    console.log('Dropping index: idx_qsos_dcl_confirmed');
+    sqlite.exec(`DROP INDEX IF EXISTS idx_qsos_dcl_confirmed`);
+
+    console.log('Dropping index: idx_qsos_qso_date');
+    sqlite.exec(`DROP INDEX IF EXISTS idx_qsos_qso_date`);
+
+    sqlite.close();
+
+    console.log('\nRollback complete! Removed 7 performance indexes.');
+    console.log('\nTo verify indexes were dropped, run:');
+    console.log('  sqlite3 award.db ".indexes qsos"');
+
+  } catch (error) {
+    console.error('Rollback failed:', error);
+    process.exit(1);
+  }
+}
+
+// Run rollback
+rollback().then(() => {
+  console.log('\nRollback script completed successfully');
+  process.exit(0);
+});