M6 — cross-compile aarch64-musl + addon.zip + install docs

scripts/build-addon-zip.sh runs the whole pipeline from a host with ssh build-host:
- one-shot messense/rust-musl-cross:aarch64-musl container builds the
  sidecar static (6.2MB stripped). Doesn't mutate the build container.
- fetches yt-dlp_linux_aarch64 from the upstream release page so Tier 2
  + Tier 3 work on the Pi (LibreELEC ships no Python YouTube tools)
- packages everything into plugin.video.torttube.zip with the Kodi
  install-from-zip layout
- drops the zip at /srv/downloads/torttube/ on the file share

Cargo.toml swaps rustypipe to default-features=false +
rustls-tls-webpki-roots so the cross-compile is openssl-free.

addon.xml drops the unused script.module.requests requirement — main.py
only uses Python stdlib + Kodi's own modules.

docs/install.md walks the Kodi UI flow + a smoke curl that fires
Player.Open via JSON-RPC. Pi-side smoke is pending install on
kodi-host.

docs/install.md

@@ -0,0 +1,65 @@
+# Installing torttube on the LibreELEC RPi
+
+The addon ships as a single `plugin.video.torttube-<version>.zip` that
+contains the Python addon, a static aarch64 sidecar binary, and yt-dlp's
+aarch64 release binary (for Tier 2/3 fallback). Nothing else needs to be
+installed on the Pi.
+
+## Build the zip (Sulkta-internal)
+
+```bash
+bash scripts/build-addon-zip.sh
+# → /srv/downloads/torttube/plugin.video.torttube-0.0.1.zip on the build host
+```
+
+The script cross-compiles the sidecar in a throwaway
+`messense/rust-musl-cross:aarch64-musl` container, fetches yt-dlp's
+official `yt-dlp_linux_aarch64` release binary, packages everything,
+drops the result at `/srv/downloads/torttube/` (file share).
+
+## Install on the Pi (Kodi UI flow)
+
+1. On the Pi: Settings → File manager → Add source → enter
+   `smb://fileserver/downloads/` → name it `downloads`.
+2. Settings → Add-ons → Install from zip file → `downloads` →
+   `torttube/plugin.video.torttube-<version>.zip`.
+3. Kodi installs, the addon appears under Video add-ons.
+
+Unsigned addons need `Settings → System → Add-ons → Unknown sources` ON.
+
+## Verify
+
+After install, fire the smoke from any LAN client:
+
+```bash
+curl -u kodi:<pw> -H "Content-Type: application/json" \
+  -X POST http://kodi-host:8080/jsonrpc -d '{
+    "jsonrpc": "2.0", "id": 1, "method": "Player.Open",
+    "params": {"item": {"file":
+      "plugin://plugin.video.torttube/?action=play&id=dQw4w9WgXcQ"}}}'
+```
+
+The TV should switch to playback of "Never Gonna Give You Up" within a
+few seconds (rustypipe resolve takes ~1s, then Kodi starts the stream).
+
+## Troubleshooting
+
+- **Black screen + "no stream URL"** notification: rustypipe returned
+  separate audio + video streams (DASH-style), and we're picking the
+  video stream which may be video-only. This is the M3 known gap —
+  needs the audio+video merge work in M3+. Workaround: try a video that
+  yt-dlp's tier-2 path can resolve to a combined format; the sidecar
+  falls back automatically.
+- **Sidecar crashes**: `cat /storage/.kodi/temp/kodi.log | grep torttube`
+  on the Pi. Sidecar logs to stderr; Kodi captures those.
+- **yt-dlp permission denied**: addon's bin/ dir needs +x. The zip
+  preserves perms but if you copied files manually, `chmod +x bin/*`.
+- **HTTPS errors from sidecar**: it bundles rustls + webpki roots, so
+  no system CA store needed. If you see "invalid certificate", your Pi
+  clock is wrong (LibreELEC's NTP failed).
+
+## Updating
+
+Just rebuild + bump the version in `addon/plugin.video.torttube/addon.xml`,
+re-run `build-addon-zip.sh`, install the new zip from the same SMB
+location. Kodi will treat it as an upgrade if the version is higher.