fix: add nolint:errcheck comments for intentionally unchecked errors

Add //nolint:errcheck comments to intentionally unchecked error returns:

- defer X.Close() calls: errors from closing read-only resources, rows
  after iteration, files, response bodies, and gzip readers are not
  actionable and don't affect correctness

- defer tx.Rollback(): standard Go pattern where rollback after
  successful commit returns an error, which is expected behavior

- defer stmt.Close(): statements are closed with their transactions

- Cleanup operations: DeleteRevision on failure and os.RemoveAll for
  temp directories are best-effort cleanup

- HTTP response encoding: if JSON encoding fails at response time,
  there's nothing useful we can do

- Test/benchmark code: unchecked errors in test setup/cleanup where
  failures will surface through test assertions

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

internal/database/postgres.go

@@ -22,7 +22,7 @@ func NewPostgresStore(connStr string) (*PostgresStore, error) {
 	}
 
 	if err := db.Ping(); err != nil {
-		db.Close()
+		db.Close() //nolint:errcheck // best-effort cleanup on connection failure
 		return nil, fmt.Errorf("failed to ping database: %w", err)
 	}
 
@@ -185,7 +185,7 @@ func (s *PostgresStore) ListRevisions(ctx context.Context) ([]*Revision, error)
 	if err != nil {
 		return nil, fmt.Errorf("failed to list revisions: %w", err)
 	}
-	defer rows.Close()
+	defer rows.Close() //nolint:errcheck // rows.Err() checked after iteration
 
 	var revisions []*Revision
 	for rows.Next() {
@@ -237,7 +237,7 @@ func (s *PostgresStore) CreateOptionsBatch(ctx context.Context, opts []*Option)
 	if err != nil {
 		return fmt.Errorf("failed to begin transaction: %w", err)
 	}
-	defer tx.Rollback()
+	defer tx.Rollback() //nolint:errcheck // rollback after commit returns error, which is expected
 
 	stmt, err := tx.PrepareContext(ctx, `
 		INSERT INTO options (revision_id, name, parent_path, type, default_value, example, description, read_only)
@@ -246,7 +246,7 @@ func (s *PostgresStore) CreateOptionsBatch(ctx context.Context, opts []*Option)
 	if err != nil {
 		return fmt.Errorf("failed to prepare statement: %w", err)
 	}
-	defer stmt.Close()
+	defer stmt.Close() //nolint:errcheck // statement closed with transaction
 
 	for _, opt := range opts {
 		err := stmt.QueryRowContext(ctx,
@@ -285,7 +285,7 @@ func (s *PostgresStore) GetChildren(ctx context.Context, revisionID int64, paren
 	if err != nil {
 		return nil, fmt.Errorf("failed to get children: %w", err)
 	}
-	defer rows.Close()
+	defer rows.Close() //nolint:errcheck // rows.Err() checked after iteration
 
 	var options []*Option
 	for rows.Next() {
@@ -357,7 +357,7 @@ func (s *PostgresStore) SearchOptions(ctx context.Context, revisionID int64, que
 	if err != nil {
 		return nil, fmt.Errorf("failed to search options: %w", err)
 	}
-	defer rows.Close()
+	defer rows.Close() //nolint:errcheck // rows.Err() checked after iteration
 
 	var options []*Option
 	for rows.Next() {
@@ -390,7 +390,7 @@ func (s *PostgresStore) CreateDeclarationsBatch(ctx context.Context, decls []*De
 	if err != nil {
 		return fmt.Errorf("failed to begin transaction: %w", err)
 	}
-	defer tx.Rollback()
+	defer tx.Rollback() //nolint:errcheck // rollback after commit returns error, which is expected
 
 	stmt, err := tx.PrepareContext(ctx, `
 		INSERT INTO declarations (option_id, file_path, line)
@@ -399,7 +399,7 @@ func (s *PostgresStore) CreateDeclarationsBatch(ctx context.Context, decls []*De
 	if err != nil {
 		return fmt.Errorf("failed to prepare statement: %w", err)
 	}
-	defer stmt.Close()
+	defer stmt.Close() //nolint:errcheck // statement closed with transaction
 
 	for _, decl := range decls {
 		err := stmt.QueryRowContext(ctx, decl.OptionID, decl.FilePath, decl.Line).Scan(&decl.ID)
@@ -419,7 +419,7 @@ func (s *PostgresStore) GetDeclarations(ctx context.Context, optionID int64) ([]
 	if err != nil {
 		return nil, fmt.Errorf("failed to get declarations: %w", err)
 	}
-	defer rows.Close()
+	defer rows.Close() //nolint:errcheck // rows.Err() checked after iteration
 
 	var decls []*Declaration
 	for rows.Next() {
@@ -460,7 +460,7 @@ func (s *PostgresStore) CreateFilesBatch(ctx context.Context, files []*File) err
 	if err != nil {
 		return fmt.Errorf("failed to begin transaction: %w", err)
 	}
-	defer tx.Rollback()
+	defer tx.Rollback() //nolint:errcheck // rollback after commit returns error, which is expected
 
 	stmt, err := tx.PrepareContext(ctx, `
 		INSERT INTO files (revision_id, file_path, extension, content, byte_size, line_count)
@@ -469,7 +469,7 @@ func (s *PostgresStore) CreateFilesBatch(ctx context.Context, files []*File) err
 	if err != nil {
 		return fmt.Errorf("failed to prepare statement: %w", err)
 	}
-	defer stmt.Close()
+	defer stmt.Close() //nolint:errcheck // statement closed with transaction
 
 	for _, file := range files {
 		// Compute metadata if not already set
@@ -516,7 +516,7 @@ func (s *PostgresStore) GetDeclarationsWithMetadata(ctx context.Context, revisio
 	if err != nil {
 		return nil, fmt.Errorf("failed to get declarations with metadata: %w", err)
 	}
-	defer rows.Close()
+	defer rows.Close() //nolint:errcheck // rows.Err() checked after iteration
 
 	var decls []*DeclarationWithMetadata
 	for rows.Next() {