v0.2.0: semaphore timeouts, error logging, dead code removal, parallel exports

Critical:
- Replace DISPATCH_TIME_FOREVER with 120s/30s timeouts in ObjC
- Log failed asset IDs and error messages in cmdExport/backupTree
- Show failed count in export summaries

Cleanup:
- Remove legacy Bridge methods (ExportAlbumPreviews, ExportAlbumOriginals, BackupAll)
- Remove legacy ObjC functions and C stub equivalents
- Remove photos.go delegates (package-level pass-throughs)
- Remove InterpretExportResult (only used by legacy methods)
- Clean up mockBridge fields (rename Fn2 -> Fn)
- Fix rc race condition in main_main.go (atomic.Int32)
- Remove unused variables (_ = grandTotal, _ = sig)

Design:
- Fix resolveAlbumID: ListAlbums first (cheap), then direct ID
- Unify Cloud type: Asset.Cloud string (was bool)
- Extract shared export logic into exportAssets/exportOne
- Add worker pool for parallel exports (3 workers when assets >= 4)
- Fix backupTree progress bar counter and directory prefix

Robustness:
- Add nil checks for stringWithUTF8String: in ObjC
- Log directory creation errors in ensure_directory (ObjC)

Quality:
- Add go vet and -race flag to Makefile test target
- Add ADR for performSelector cloudIdentifier decision
- Add sync comments between Go/ObjC sanitizePathComponent
- Add package-level doc comment
- Add tests: partial failure, skipped album, album-not-found message

internal/photos/photos.go

@@ -1,36 +1,8 @@
+// Package photos provides a Go bridge to Apple's PhotoKit framework via CGo,
+// enabling programmatic access to photos, albums, and export operations.
 package photos
 
 import "fmt"
 
 var errAccessDenied = fmt.Errorf("photos access denied: grant Full Disk Access or Photos permission in System Settings > Privacy & Security")
-var errBridgeNil = fmt.Errorf("bridge returned nil")
-
-func RequestAccess() error { return DefaultBridge.RequestAccess() }
-
-func ListAlbums() ([]Album, error) { return DefaultBridge.ListAlbums() }
-
-func ListAssets(albumID string) ([]Asset, int, error) { return DefaultBridge.ListAssets(albumID) }
-
-func ListTree() ([]CollectionNode, error) { return DefaultBridge.ListTree() }
-
-func ExportAlbumPreviews(albumID, outputDir string, targetSize int) (int, error) {
-	return DefaultBridge.ExportAlbumPreviews(albumID, outputDir, targetSize)
-}
-
-func ExportAlbumOriginals(albumID, outputDir string) (int, error) {
-	return DefaultBridge.ExportAlbumOriginals(albumID, outputDir)
-}
-
-func BackupAll(outputDir string, targetSize int, originals bool) (int, error) {
-	return DefaultBridge.BackupAll(outputDir, targetSize, originals)
-}
-
-func Cancel() { DefaultBridge.Cancel() }
-
-func ExportPreview(assetID, outputDir string, targetSize, index int) (ExportResult, error) {
-	return DefaultBridge.ExportPreview(assetID, outputDir, targetSize, index)
-}
-
-func ExportOriginal(assetID, outputDir string, index int) (ExportResult, error) {
-	return DefaultBridge.ExportOriginal(assetID, outputDir, index)
-}
+var errBridgeNil = fmt.Errorf("bridge returned nil")