refactor: consolidate the duplicated download and worker-pool code

internal/download
  The ~40-line progress-bar decorator stack was copy-pasted into three download
  paths and had started to drift; it is now newDownloadBar, which returns a nil
  bar when progress is off (so callers use it unconditionally) plus a finish
  func to defer. The three hand-rolled read/write loops that differed only in
  whether they touched a bar become copyWithProgress.

  FileDeezerEncrypted and FileYandexEncrypted were ~90% identical: mkdir, GET,
  status check, create output, bar, cleanup-on-failure, Content-Length check,
  fsync. That scaffolding is now streamEncrypted, and each function supplies
  only its decryption step. Also switches the io.EOF/io.ErrUnexpectedEOF
  comparisons to errors.Is.

internal/app
  Three copies of "coerce a JSON array that may be []any or []map[string]any"
  become anySlice, which also reports whether the value was an array at all so
  callers can still distinguish missing from empty.

  The worker-pool dispatch existed three times and the copies disagreed: two
  counted failures under a mutex and logged inline with the track id, while the
  third collected errors in a channel and logged them all after wg.Wait()
  without the id. runTrackWorkers unifies them on the inline form, which
  reports failures as they happen and names the track, and keeps the mutex held
  across the log so failure lines cannot interleave.

Tests
  The progress-bar paths had no coverage at all, because progress is disabled
  when not attached to a terminal; four new tests force it on via the existing
  STREAMRIP_GO_FORCE_PROGRESS escape hatch and cover the determinate bar, the
  unknown-length spinner, Deezer decryption with a bar attached, and the
  failure path still removing the partial file. internal/download coverage
  53% -> 63%.

  Three cancellation tests pin the Ctrl-C fix. Verified as genuine regression
  tests by reverting the guards: without them the rip walks all 40 tracks of a
  cancelled album, logs a failure for each, and Rip() returns nil.

Adds store.SQLite.IsFailed, the read complement to MarkFailed, used by the
bookkeeping test to confirm failure records still land under a cancelled
context.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

internal/download/downloader_test.go

@@ -1,6 +1,7 @@
 package download
 
 import (
+	"bytes"
 	"context"
 	"crypto/aes"
 	"crypto/cipher"
@@ -12,6 +13,7 @@ import (
 	"os"
 	"os/exec"
 	"path/filepath"
+	"strconv"
 	"strings"
 	"testing"
 	"time"
@@ -367,3 +369,144 @@ func containsArgPair(args []string, key, value string) bool {
 	}
 	return false
 }
+
+// newProgressDownloader builds a Downloader with the progress bars actually
+// enabled. The bar code paths are otherwise never exercised, because tests do
+// not run on a terminal; STREAMRIP_GO_FORCE_PROGRESS is the documented escape
+// hatch. Output goes to stderr, which `go test` captures.
+func newProgressDownloader(t *testing.T) *Downloader {
+	t.Helper()
+	t.Setenv("STREAMRIP_GO_FORCE_PROGRESS", "1")
+	d := NewWithOptions(true, true, 0)
+	if !d.ProgressEnabled() {
+		t.Fatal("expected progress to be enabled")
+	}
+	t.Cleanup(d.Close)
+	return d
+}
+
+// TestFileWithProgressBar covers the determinate-bar path (Content-Length
+// known) through the shared newDownloadBar/copyWithProgress helpers.
+func TestFileWithProgressBar(t *testing.T) {
+	payload := bytes.Repeat([]byte("abcd"), 4096)
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		w.Header().Set("Content-Length", strconv.Itoa(len(payload)))
+		_, _ = w.Write(payload)
+	}))
+	defer ts.Close()
+
+	d := newProgressDownloader(t)
+	out := filepath.Join(t.TempDir(), "sub", "a.flac")
+	if err := d.File(context.Background(), ts.URL, out); err != nil {
+		t.Fatalf("File() error = %v", err)
+	}
+	got, err := os.ReadFile(out)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(got, payload) {
+		t.Fatalf("content mismatch: got %d bytes, want %d", len(got), len(payload))
+	}
+}
+
+// TestFileWithSpinnerUnknownLength covers the spinner path, taken when the
+// server does not send a Content-Length.
+func TestFileWithSpinnerUnknownLength(t *testing.T) {
+	payload := bytes.Repeat([]byte("xyz"), 3000)
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		w.Header().Set("Transfer-Encoding", "chunked")
+		_, _ = w.Write(payload)
+	}))
+	defer ts.Close()
+
+	d := newProgressDownloader(t)
+	out := filepath.Join(t.TempDir(), "a.flac")
+	if err := d.File(context.Background(), ts.URL, out); err != nil {
+		t.Fatalf("File() error = %v", err)
+	}
+	got, err := os.ReadFile(out)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(got, payload) {
+		t.Fatalf("content mismatch: got %d bytes, want %d", len(got), len(payload))
+	}
+}
+
+// TestFileDeezerEncryptedWithProgressBar runs the Deezer decryption through
+// the progress-enabled path, so the shared streamEncrypted scaffolding is
+// covered with a bar attached as well as without.
+func TestFileDeezerEncryptedWithProgressBar(t *testing.T) {
+	plain := make([]byte, deezerBFChunkSize*4+100)
+	for i := range plain {
+		plain[i] = byte((i * 7) % 253)
+	}
+	trackID := "123456"
+	enc := encryptDeezerPayload(t, plain, trackID)
+
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		w.Header().Set("Content-Length", strconv.Itoa(len(enc)))
+		_, _ = w.Write(enc)
+	}))
+	defer ts.Close()
+
+	d := newProgressDownloader(t)
+	out := filepath.Join(t.TempDir(), "a.mp3")
+	if err := d.FileDeezerEncrypted(context.Background(), ts.URL, out, trackID); err != nil {
+		t.Fatalf("FileDeezerEncrypted() error = %v", err)
+	}
+	got, err := os.ReadFile(out)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(got, plain) {
+		t.Fatal("decrypted output does not match the original plaintext")
+	}
+}
+
+// encryptDeezerPayload applies Deezer's scheme: Blowfish-CBC on every third
+// full 2048-byte chunk, everything else left in the clear.
+func encryptDeezerPayload(t *testing.T, plain []byte, trackID string) []byte {
+	t.Helper()
+	block, err := blowfish.NewCipher(deriveDeezerBlowfishKey(defaultDeezerBlowfishSecret, trackID))
+	if err != nil {
+		t.Fatal(err)
+	}
+	enc := make([]byte, len(plain))
+	copy(enc, plain)
+	for i, off := 0, 0; off < len(plain); i, off = i+1, off+deezerBFChunkSize {
+		end := off + deezerBFChunkSize
+		if end > len(plain) {
+			break
+		}
+		if i%3 != 0 {
+			continue
+		}
+		mode := cipher.NewCBCEncrypter(block, deezerBFIV)
+		mode.CryptBlocks(enc[off:end], plain[off:end])
+	}
+	return enc
+}
+
+// TestProgressBarFailurePathRemovesPartialFile checks that a mid-download
+// failure still runs the bar cleanup and removes the partial output, which is
+// the behaviour the finishBar(success) defer replaced.
+func TestProgressBarFailurePathRemovesPartialFile(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		w.Header().Set("Content-Length", "100000")
+		_, _ = w.Write(bytes.Repeat([]byte("a"), 10))
+		if f, ok := w.(http.Flusher); ok {
+			f.Flush()
+		}
+	}))
+	defer ts.Close()
+
+	d := newProgressDownloader(t)
+	out := filepath.Join(t.TempDir(), "a.flac")
+	if err := d.File(context.Background(), ts.URL, out); err == nil {
+		t.Fatal("expected a truncated-response error")
+	}
+	if _, err := os.Stat(out); !os.IsNotExist(err) {
+		t.Fatalf("partial file not removed, stat err = %v", err)
+	}
+}