perf: run yt-dlp from a zipapp on a portable Python

Replaces the official yt-dlp_macos sidecar. That build is PyInstaller
one-file and unpacks 37MB on every invocation, costing ~8s per call on
this machine — ruled out signing, xattrs and thinning the universal
binary as causes, and it is 8% CPU over 8s, so it is the unpack itself.
Every stream resolve paid it.

The 3MB zipapp on a trimmed portable CPython starts in ~0.45s, a 17x
improvement; a real stream resolve goes from ~10s to ~2.4s. macOS ships
only Python 3.9 and yt-dlp needs 3.10+, hence bundling an interpreter.

yt-dlp is now resolved as an argv prefix rather than a path, so a system
install (a plain script, instant) still takes precedence.

Bundle grows 153MB -> 219MB, which buys back the responsiveness.

src-tauri/tauri.conf.json

@@ -45,9 +45,12 @@
       "icons/icon.ico"
     ],
     "externalBin": [
-      "binaries/yt-dlp",
       "binaries/ffmpeg",
       "binaries/ffprobe"
-    ]
+    ],
+    "resources": {
+      "resources/python": "python",
+      "resources/yt-dlp.pyz": "yt-dlp.pyz"
+    }
   }
 }