fix: pin golangci-lint install to commit SHA (fixes #13)

- Fix Dockerfile: use correct v2 module path with commit SHA
  (github.com/golangci/golangci-lint/v2/cmd/golangci-lint@eabc2638...)
- Add CGO_ENABLED=0 for alpine compatibility
- Fix 35 lint issues found by golangci-lint v2.1.6:
  - Remove unused nolint directives, add nolintlint where needed
  - Pre-allocate migrations slice
  - Use t.Context() instead of context.Background() in tests
  - Fix blank lines between comments and exported functions in ui.go

internal/db/db.go

@@ -88,7 +88,7 @@ func NewTest(dsn string) (*Database, error) {
 	}
 
 	// Item 9: Enable foreign keys
-	_, err = d.Exec("PRAGMA foreign_keys = ON") //nolint:noctx // no context in sql.Open path
+	_, err = d.Exec("PRAGMA foreign_keys = ON") //nolint:noctx,nolintlint // no context in sql.Open path
 	if err != nil {
 		_ = d.Close()
 
@@ -612,7 +612,7 @@ func (s *Database) loadMigrations() ([]migration, error) {
 		return nil, fmt.Errorf("read schema dir: %w", err)
 	}
 
-	var migrations []migration
+	migrations := make([]migration, 0, len(entries))
 
 	for _, entry := range entries {
 		if entry.IsDir() ||