M0 scaffold — Python addon + Rust sidecar

Kodi addon (plugin.video.torttube) shell with Cargo workspace for the
rustypipe-backed sidecar binary. No working extraction yet — addon.xml
parses, main.py is a notification stub, sidecar's main.rs prints scaffold
banner. See MILESTONES.md for M1..M6.

License: GPL-3.0-or-later (matches rustypipe + NewPipeExtractor).

README.md

@@ -0,0 +1,43 @@
+# torttube
+
+Kodi addon for YouTube via [RustyPipe](https://codeberg.org/ThetaDev/rustypipe)
+extraction + [SponsorBlock](https://sponsor.ajay.app/) segment skipping.
+
+Replaces the dead `plugin.video.youtube` on LibreELEC RPi TVs after Google
+required account-linking for the upstream addon.
+
+## Architecture
+
+```
+Kodi (LibreELEC, RPi)
+  └── plugin.video.torttube     [Python addon — UI, browse, settings]
+        └── torttube-sidecar    [Rust binary — Innertube extraction,
+                                 SponsorBlock fetch, JSON-over-stdio]
+              ├── rustypipe     [YouTube Innertube client + sig decode]
+              └── sponsorblock  [REST API client, SHA-256 prefix lookup]
+```
+
+Kodi addons are Python — the engine layer (n-param sig decoding, Innertube,
+SponsorBlock hashing) lives in a Rust sidecar so we get a single maintained
+extraction surface and clean aarch64/armv7 cross-compiles.
+
+## Status
+
+M0 scaffold. Nothing playable yet — see [MILESTONES.md](MILESTONES.md).
+
+## Upstream contributions
+
+NewPipeExtractor (Java) is the canonical reference for Innertube behaviour.
+When we hit a corner case RustyPipe doesn't cover we look at NPE for the
+fix, then either port it to RustyPipe (Rust PR) or fix NPE directly (Java
+PR). Either way upstream lands a real improvement.
+
+Issues we're watching:
+- [NPE #1339](https://github.com/TeamNewPipe/NewPipeExtractor/issues/1339) — n-parameter deobfuscation
+- [NPE #1444](https://github.com/TeamNewPipe/NewPipeExtractor/issues/1444) — distinguish unavailable vs unextractable
+- [NPE #1360](https://github.com/TeamNewPipe/NewPipeExtractor/issues/1360) — refactor link handlers (help wanted)
+- [NPE #1357](https://github.com/TeamNewPipe/NewPipeExtractor/issues/1357) — JDoc checks in PR pipeline (good first issue)
+
+## License
+
+GPL-3.0-or-later. Matches RustyPipe and NewPipeExtractor.