fix(macos): hard-fail bundle without mpv, PATH fallback, CI mpv install

- build.ts: darwin compile now exits 1 when mpv is absent — CI can no
  longer ship a PodTui.app without its bundled player (0.4.0 did, killing
  Now Playing attribution).
- audio-player.ts: the bundled mpv is probed (--version) at first resolve;
  it links against brew's dylibs, and a Homebrew ffmpeg major upgrade can
  break it — fall back to PATH mpv so audio survives (icon degrades to
  blank instead of playback dying). Probed once per process.
- release.yml: brew install mpv on darwin runners; smoke test now asserts
  the tarball's PodTui.app has a launchable mpv signed with the
  com.mikefreno.podtui identifier.

.github/workflows/release.yml

@@ -50,7 +50,10 @@ jobs:
       - name: Install fftw (cavacore build dependency)
         run: |
           if uname -s | grep -qi darwin; then
-            brew install fftw
+            # mpv is required for the release bundle: build.ts copies it into
+            # PodTui.app (signed with the podtui bundle identifier) so macOS
+            # Now Playing shows the PodTui icon instead of a blank placeholder.
+            brew install fftw mpv
           else
             sudo apt-get update
             sudo apt-get install -y libfftw3-dev
@@ -76,6 +79,16 @@ jobs:
           printf 'preload = ["./definitely-missing.ts"]\n' > "$SMOKE_DIR/bunfig.toml"
           cd "$SMOKE_DIR"
           ./podtui-*/podtui --version
+          # macOS tarballs must ship PodTui.app with a working bundled mpv
+          # carrying the podtui bundle identifier — otherwise Now Playing
+          # attribution silently regresses to a blank icon.
+          if [ "${{ matrix.plat }}" = "darwin" ]; then
+            MPV=./podtui-*/PodTui.app/Contents/MacOS/mpv
+            test -x $MPV || { echo "PodTui.app missing bundled mpv"; exit 1; }
+            $MPV --version >/dev/null || { echo "bundled mpv does not launch"; exit 1; }
+            codesign -dvv $MPV 2>&1 | grep -q "Identifier=com.mikefreno.podtui" \
+              || { echo "bundled mpv lacks podtui signing identifier"; exit 1; }
+          fi
 
       - name: Upload artifact
         uses: actions/upload-artifact@v6