Fix SQLite transaction deadlocks with immediate mode

- Add _txlock=immediate to SQLite connection string
- This prevents deadlocks by acquiring write locks at transaction start
- Multiple concurrent writers now queue properly instead of failing instantly
- Resolves 'database table is locked' errors in production

internal/database/database.go

@@ -62,7 +62,11 @@ func New(cfg *config.Config, logger *logger.Logger) (*Database, error) {
 
 	// Add connection parameters for go-sqlite3
 	// Enable WAL mode and other performance optimizations
-	dsn := fmt.Sprintf("file:%s?_busy_timeout=5000&_journal_mode=WAL&_synchronous=OFF&cache=shared", dbPath)
+	// Use immediate transactions to prevent deadlocks when multiple writers compete
+	dsn := fmt.Sprintf(
+		"file:%s?_busy_timeout=5000&_journal_mode=WAL&_synchronous=OFF&cache=shared&_txlock=immediate",
+		dbPath,
+	)
 	db, err := sql.Open("sqlite3", dsn)
 	if err != nil {
 		return nil, fmt.Errorf("failed to open database: %w", err)