Centralize error handling patterns in storage layer (bd-bwk2)

Standardized error handling across the SQLite storage layer by
consistently using wrapDBError() helper functions that were already
defined in errors.go.

Changes:
- config.go: Applied wrapDBError to all config/metadata functions
- queries.go: Fixed bare 'return err' in CreateIssue, UpdateIssue, DeleteIssues
- store.go: Changed %v to %w for proper error chain preservation
- errors_test.go: Added comprehensive test coverage for error wrapping

All error paths now:
- Wrap errors with operation context using %w
- Convert sql.ErrNoRows to ErrNotFound consistently
- Preserve error chains for unwrapping and type checking

This improves debugging by maintaining operation context throughout
the error chain and enables type-safe error checking with sentinel
errors.

All tests passing ✓

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

internal/storage/sqlite/store.go

@@ -149,7 +149,7 @@ func New(ctx context.Context, path string) (*SQLiteStorage, error) {
 	if err := verifySchemaCompatibility(db); err != nil {
 		// Schema probe failed - retry migrations once
 		if retryErr := RunMigrations(db); retryErr != nil {
-			return nil, fmt.Errorf("migration retry failed after schema probe failure: %w (original: %v)", retryErr, err)
+			return nil, fmt.Errorf("migration retry failed after schema probe failure: %w (original: %w)", retryErr, err)
 		}
 
 		// Probe again after retry