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

cmd/photoscli/main_main.go

@@ -3,6 +3,7 @@ package main
 import (
 	"os"
 	"os/signal"
+	"sync/atomic"
 	"syscall"
 
 	"gitea.k3s.k0.nu/tools/photocli/internal/photos"
@@ -15,21 +16,20 @@ func main() {
 	signal.Notify(sigCh, syscall.SIGINT, syscall.SIGTERM)
 
 	done := make(chan struct{})
-	var rc int
+	var rc atomic.Int32
 
 	go func() {
-		rc = run(os.Args[1:], os.Stdout, os.Stderr, photos.DefaultBridge)
+		rc.Store(int32(run(os.Args[1:], os.Stdout, os.Stderr, photos.DefaultBridge)))
 		close(done)
 	}()
 
 	select {
 	case <-done:
-	case sig := <-sigCh:
+	case <-sigCh:
 		photos.DefaultBridge.Cancel()
 		os.Stderr.Write([]byte("\nreceived signal, finishing current file...\n"))
 		<-done
-		_ = sig
 	}
 
-	os.Exit(rc)
+	os.Exit(int(rc.Load()))
 }