M6 DONE — torttube ships, Rick Astley plays fullscreen on the Livingroom Pi

Live install verified end-to-end:
- SSH'd into 192.168.0.158 (LibreELEC, Kodi 20.3 Nexus, kernel aarch64
  / userspace armhf — that's why the static Rust sidecar runs but the
  PyInstaller yt-dlp binary couldn't)
- Dropped addon dir into /storage/.kodi/addons/
- systemctl restart kodi → Kodi rescans /storage/.kodi/addons/
- JSON-RPC Addons.SetAddonEnabled flipped enabled:false → true
- Player.Open with plugin URL → 7s yt-dlp resolve → VideoFullScreen.xml,
  fullscreen:true, currentwindow 12005, audio+video synced

Fixes that surfaced during the install:
- yt-dlp swap: PyInstaller aarch64 binary needs ld-linux-aarch64.so.1
  which LibreELEC doesn't ship. Switched to the universal Python zipapp
  (~3MB) which runs on /usr/bin/python3.11. build-addon-zip.sh updated.
- main.py now puts the addon's bin/ dir on PATH so the sidecar's
  Command::new('yt-dlp') call resolves to the bundled zipapp.
- Cosmetic fix: resolve.rs's classify_yt_dlp_error preserves the
  original error message (was downcasing it for keyword matching and
  then using the lowercased copy as the user-facing error).

Caveats logged for later:
- 360p ceiling (yt-dlp '-f best[ext=mp4]' picks itag 18; 720p
  progressive itag 22 is deprecated by YouTube; higher quality wants
  DASH manifest generation).
- ALSA sink: device 'sysdefault:CARD=vc4hdmi1' fails to open on this
  Pi but Kodi auto-falls-back to 'sysdefault' so audio works. Worth
  cleaning up in Kodi audio settings later.

MILESTONES + docs/install.md updated with the SSH + JSON-RPC alternate
install path.

docs/install.md

@@ -27,6 +27,25 @@ drops the result at `/mnt/user/downloads/torttube/` (Lucy SMB).
 
 Unsigned addons need `Settings → System → Add-ons → Unknown sources` ON.
 
+## Install via SSH + JSON-RPC (no UI needed)
+
+If SSH is enabled (`Settings → Services → SSH`):
+
+```bash
+# from any LAN host with ssh access to the Pi
+scp plugin.video.torttube-0.0.1.zip kodi-host:/tmp/
+ssh kodi-host 'cd /storage/.kodi/addons && unzip -o /tmp/plugin.video.torttube-0.0.1.zip && chmod +x plugin.video.torttube/bin/*'
+ssh kodi-host 'systemctl restart kodi'
+
+# wait ~5s for Kodi to come back, then enable the addon
+curl -u kodi:<pw> -H "Content-Type: application/json" -X POST http://<kodi-host>:8080/jsonrpc \
+  -d '{"jsonrpc":"2.0","id":1,"method":"Addons.SetAddonEnabled","params":{"addonid":"plugin.video.torttube","enabled":true}}'
+```
+
+Freshly-installed addons land in Kodi's database as `enabled:false` —
+the SetAddonEnabled call above flips that. Without it, Player.Open with
+the plugin URL fails silently with "Unable to find plugin" in kodi.log.
+
 ## Verify
 
 After install, fire the smoke from any LAN client: