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.

scripts/fetch-binaries.sh

@@ -1,35 +1,59 @@
 #!/usr/bin/env bash
-# Fetches the helper binaries FlightTube ships as Tauri sidecars.
+# Fetches the helper tools FlightTube ships inside its bundle.
 #
-# They are not in git — together they are about 140MB. Run this once before
-# building, or after changing the target architecture.
+# They are not in git (~130MB together). Run this once before building.
+#
+#   ffmpeg / ffprobe  static arm64 binaries, shipped as Tauri sidecars
+#   python + yt-dlp   a portable interpreter plus the yt-dlp zipapp
+#
+# yt-dlp is deliberately NOT the official yt-dlp_macos build: that is a
+# PyInstaller one-file binary which unpacks ~37MB on every invocation, costing
+# about eight seconds per call. The 3MB zipapp on a portable interpreter starts
+# in under half a second. macOS ships only Python 3.9 and yt-dlp needs 3.10+,
+# which is why the interpreter has to come along.
 set -euo pipefail
 
 TRIPLE="${1:-aarch64-apple-darwin}"
-DEST="$(cd "$(dirname "$0")/.." && pwd)/src-tauri/binaries"
+ROOT="$(cd "$(dirname "$0")/.." && pwd)"
+BIN="$ROOT/src-tauri/binaries"
+RES="$ROOT/src-tauri/resources"
 TMP="$(mktemp -d)"
 trap 'rm -rf "$TMP"' EXIT
-mkdir -p "$DEST"
+mkdir -p "$BIN" "$RES"
 
-echo "Fetching yt-dlp (official GitHub release)…"
-curl -fsSL -o "$TMP/yt-dlp" \
-  https://github.com/yt-dlp/yt-dlp/releases/latest/download/yt-dlp_macos
-
-# Static arm64 builds; Homebrew's ffmpeg links a dozen dylibs and cannot be
-# relocated into an app bundle.
+echo "Fetching ffmpeg and ffprobe (static arm64)…"
+# Homebrew's ffmpeg links a dozen dylibs and cannot be relocated into a bundle.
 for tool in ffmpeg ffprobe; do
-  echo "Fetching $tool (static, osxexperts.net)…"
   curl -fsSL -A "Mozilla/5.0" -o "$TMP/$tool.zip" "https://www.osxexperts.net/${tool}9arm.zip"
   unzip -o -q "$TMP/$tool.zip" -d "$TMP"
+  install -m 0755 "$TMP/$tool" "$BIN/$tool-$TRIPLE"
 done
 
-for tool in yt-dlp ffmpeg ffprobe; do
-  install -m 0755 "$TMP/$tool" "$DEST/$tool-$TRIPLE"
-  echo "  -> $DEST/$tool-$TRIPLE"
-done
+echo "Fetching the yt-dlp zipapp…"
+curl -fsSL -o "$RES/yt-dlp.pyz" \
+  https://github.com/yt-dlp/yt-dlp/releases/latest/download/yt-dlp
 
-echo "Done. Verifying they run:"
-for tool in yt-dlp ffmpeg ffprobe; do
-  "$DEST/$tool-$TRIPLE" -version 2>/dev/null | head -1 || \
-  "$DEST/$tool-$TRIPLE" --version 2>/dev/null | head -1
-done
+echo "Fetching a portable Python…"
+PY_TAG="$(curl -fsSL -H 'User-Agent: flighttube-build' \
+  https://api.github.com/repos/astral-sh/python-build-standalone/releases/latest \
+  | python3 -c 'import json,sys; print(json.load(sys.stdin)["tag_name"])')"
+PY_ASSET="cpython-3.12.14+${PY_TAG}-${TRIPLE}-install_only_stripped.tar.gz"
+curl -fsSL -o "$TMP/python.tar.gz" \
+  "https://github.com/astral-sh/python-build-standalone/releases/download/${PY_TAG}/${PY_ASSET// /%20}"
+rm -rf "$RES/python"
+tar -xzf "$TMP/python.tar.gz" -C "$TMP"
+mv "$TMP/python" "$RES/python"
+
+echo "Trimming the interpreter to what yt-dlp needs…"
+P="$RES/python"
+rm -rf "$P/include" "$P/share" "$P/lib/pkgconfig" \
+       "$P/lib/python3.12/test" "$P/lib/python3.12/idlelib" \
+       "$P/lib/python3.12/tkinter" "$P/lib/python3.12/lib2to3" \
+       "$P/lib/python3.12/ensurepip" "$P/lib/python3.12/turtledemo" \
+       "$P/lib/python3.12/config-3.12-darwin"
+find "$P" -name "libpython*.a" -delete
+find "$P" -name "__pycache__" -type d -prune -exec rm -rf {} + 2>/dev/null || true
+
+echo "Verifying:"
+"$BIN/ffmpeg-$TRIPLE" -version | head -1
+"$P/bin/python3.12" "$RES/yt-dlp.pyz" --version