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

Makefile

@@ -1,6 +1,6 @@
 BINARY     := ./bin/photoscli
 MODULE     := gitea.k3s.k0.nu/tools/photocli
-VERSION    := 0.1.0
+VERSION    := 0.2.0
 BRIDGE_DIR := bridge
 LDFLAGS    := -X main.version=$(VERSION)
 OBJ        := $(BRIDGE_DIR)/photokit_bridge.o
@@ -30,7 +30,8 @@ build: $(LIB)
 	go build -ldflags "$(LDFLAGS)" -o $(BINARY) $(MODULE)/cmd/photoscli
 
 test: $(STUB_LIB)
-	go test -tags=test -coverprofile=coverage.out -covermode=atomic -coverpkg=./... ./...
+	go vet -tags=test ./...
+	go test -tags=test -race -coverprofile=coverage.out -covermode=atomic -coverpkg=./... ./...
 	@grep -v 'main_main.go' coverage.out > coverage_filtered.out 2>/dev/null || true
 	@mv coverage_filtered.out coverage.out 2>/dev/null || true
 	@go tool cover -func=coverage.out | tail -1