feat(clients/decky): SteamOS Gaming-Mode launcher plugin (spike)

A Decky Loader plugin so a Steam Deck / SteamOS box can launch the punktfunk
client from Gaming Mode using REAL Steam UI components (it runs inside Steam's
CEF, so the panel is built from @decky/ui — the literal Big Picture primitives,
not a replica).

- Frontend (src/index.tsx, @decky/api + @decky/ui): a Quick Access Menu panel —
  Refresh → discover hosts, a native list (name, ip:port, pairing flag), tap to
  connect with a status toast, Disconnect.
- Backend (main.py): discover() shells `avahi-browse -rpt _punktfunk._udp` and
  parses the host's advertised TXT keys (proto/fp/pair/id from discovery.rs),
  dedup by id preferring IPv4; connect() resolves + spawns
  `punktfunk-client --connect host:port` (gamescope composites its video like a
  game), tracking the child; disconnect() terminates it.
- Mirrors the current official Decky template (the API moved to @decky/ui +
  @decky/api). Frontend builds clean (pnpm build → dist/index.js); main.py
  py_compiles. dist/ + node_modules gitignored — build on the Deck per README.

Spike scope: launcher only, runtime untested (no Deck here). Next on this track:
the in-stream Quick-Access overlay (volume/disconnect/stats over the running
stream) and a fuller real-components UI. Client decode on the AMD Deck is the
existing VAAPI path; the host-encode VAAPI gap is separate (NVIDIA host = NVENC).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

clients/decky/rollup.config.js

@@ -0,0 +1,5 @@
+import deckyPlugin from "@decky/rollup";
+
+export default deckyPlugin({
+  // Add your extra Rollup options here
+});