fix: rebase onto main, fix SQLite concurrency, lint clean

- Add busy_timeout PRAGMA and MaxOpenConns(1) for SQLite stability
- Use per-test temp DB in handler tests to prevent state leaks
- Pre-allocate migrations slice (prealloc lint)
- Remove invalid linter names (wsl_v5, noinlineerr) from .golangci.yml
- Remove unused //nolint:gosec directives
- Replace context.Background() with t.Context() in tests
- Use goimports formatting for all files
- All make check passes with zero failures

internal/db/db.go

@@ -81,7 +81,7 @@ func (s *Database) GetDB() *sql.DB {
 func (s *Database) connect(ctx context.Context) error {
 	dbURL := s.params.Config.DBURL
 	if dbURL == "" {
-		dbURL = "file:./data.db?_journal_mode=WAL"
+		dbURL = "file:./data.db?_journal_mode=WAL&_busy_timeout=5000"
 	}
 
 	s.log.Info("connecting to database", "url", dbURL)
@@ -104,6 +104,8 @@ func (s *Database) connect(ctx context.Context) error {
 		return err
 	}
 
+	d.SetMaxOpenConns(1)
+
 	s.db = d
 	s.log.Info("database connected")
 
@@ -114,6 +116,13 @@ func (s *Database) connect(ctx context.Context) error {
 		return fmt.Errorf("enable foreign keys: %w", err)
 	}
 
+	_, err = s.db.ExecContext(
+		ctx, "PRAGMA busy_timeout = 5000",
+	)
+	if err != nil {
+		return fmt.Errorf("set busy timeout: %w", err)
+	}
+
 	return s.runMigrations(ctx)
 }
 
@@ -233,7 +242,7 @@ func (s *Database) loadMigrations() (
 		)
 	}
 
-	var migrations []migration
+	migrations := make([]migration, 0, len(entries))
 
 	for _, entry := range entries {
 		if entry.IsDir() ||