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/decky.pyi

@@ -0,0 +1,184 @@
+"""
+This module exposes various constants and helpers useful for decky plugins.
+
+* Plugin's settings and configurations should be stored under `DECKY_PLUGIN_SETTINGS_DIR`.
+* Plugin's runtime data should be stored under `DECKY_PLUGIN_RUNTIME_DIR`.
+* Plugin's persistent log files should be stored under `DECKY_PLUGIN_LOG_DIR`.
+
+Avoid writing outside of `DECKY_HOME`, storing under the suggested paths is strongly recommended.
+
+Some basic migration helpers are available: `migrate_any`, `migrate_settings`, `migrate_runtime`, `migrate_logs`.
+
+A logging facility `logger` is available which writes to the recommended location.
+"""
+
+__version__ = '1.0.0'
+
+import logging
+
+from typing import Any
+
+"""
+Constants
+"""
+
+HOME: str
+"""
+The home directory of the effective user running the process.
+Environment variable: `HOME`.
+If `root` was specified in the plugin's flags it will be `/root` otherwise the user whose home decky resides in.
+e.g.: `/home/deck`
+"""
+
+USER: str
+"""
+The effective username running the process.
+Environment variable: `USER`.
+It would be `root` if `root` was specified in the plugin's flags otherwise the user whose home decky resides in.
+e.g.: `deck`
+"""
+
+DECKY_VERSION: str
+"""
+The version of the decky loader.
+Environment variable: `DECKY_VERSION`.
+e.g.: `v2.5.0-pre1`
+"""
+
+DECKY_USER: str
+"""
+The user whose home decky resides in.
+Environment variable: `DECKY_USER`.
+e.g.: `deck`
+"""
+
+DECKY_USER_HOME: str
+"""
+The home of the user where decky resides in.
+Environment variable: `DECKY_USER_HOME`.
+e.g.: `/home/deck`
+"""
+
+DECKY_HOME: str
+"""
+The root of the decky folder.
+Environment variable: `DECKY_HOME`.
+e.g.: `/home/deck/homebrew`
+"""
+
+DECKY_PLUGIN_SETTINGS_DIR: str
+"""
+The recommended path in which to store configuration files (created automatically).
+Environment variable: `DECKY_PLUGIN_SETTINGS_DIR`.
+e.g.: `/home/deck/homebrew/settings/decky-plugin-template`
+"""
+
+DECKY_PLUGIN_RUNTIME_DIR: str
+"""
+The recommended path in which to store runtime data (created automatically).
+Environment variable: `DECKY_PLUGIN_RUNTIME_DIR`.
+e.g.: `/home/deck/homebrew/data/decky-plugin-template`
+"""
+
+DECKY_PLUGIN_LOG_DIR: str
+"""
+The recommended path in which to store persistent logs (created automatically).
+Environment variable: `DECKY_PLUGIN_LOG_DIR`.
+e.g.: `/home/deck/homebrew/logs/decky-plugin-template`
+"""
+
+DECKY_PLUGIN_DIR: str
+"""
+The root of the plugin's directory.
+Environment variable: `DECKY_PLUGIN_DIR`.
+e.g.: `/home/deck/homebrew/plugins/decky-plugin-template`
+"""
+
+DECKY_PLUGIN_NAME: str
+"""
+The name of the plugin as specified in the 'plugin.json'.
+Environment variable: `DECKY_PLUGIN_NAME`.
+e.g.: `Example Plugin`
+"""
+
+DECKY_PLUGIN_VERSION: str
+"""
+The version of the plugin as specified in the 'package.json'.
+Environment variable: `DECKY_PLUGIN_VERSION`.
+e.g.: `0.0.1`
+"""
+
+DECKY_PLUGIN_AUTHOR: str
+"""
+The author of the plugin as specified in the 'plugin.json'.
+Environment variable: `DECKY_PLUGIN_AUTHOR`.
+e.g.: `John Doe`
+"""
+
+DECKY_PLUGIN_LOG: str
+"""
+The path to the plugin's main logfile.
+Environment variable: `DECKY_PLUGIN_LOG`.
+e.g.: `/home/deck/homebrew/logs/decky-plugin-template/plugin.log`
+"""
+
+"""
+Migration helpers
+"""
+
+
+def migrate_any(target_dir: str, *files_or_directories: str) -> dict[str, str]:
+    """
+    Migrate files and directories to a new location and remove old locations.
+    Specified files will be migrated to `target_dir`.
+    Specified directories will have their contents recursively migrated to `target_dir`.
+
+    Returns the mapping of old -> new location.
+    """
+
+
+def migrate_settings(*files_or_directories: str) -> dict[str, str]:
+    """
+    Migrate files and directories relating to plugin settings to the recommended location and remove old locations.
+    Specified files will be migrated to `DECKY_PLUGIN_SETTINGS_DIR`.
+    Specified directories will have their contents recursively migrated to `DECKY_PLUGIN_SETTINGS_DIR`.
+
+    Returns the mapping of old -> new location.
+    """
+
+
+def migrate_runtime(*files_or_directories: str) -> dict[str, str]:
+    """
+    Migrate files and directories relating to plugin runtime data to the recommended location and remove old locations
+    Specified files will be migrated to `DECKY_PLUGIN_RUNTIME_DIR`.
+    Specified directories will have their contents recursively migrated to `DECKY_PLUGIN_RUNTIME_DIR`.
+
+    Returns the mapping of old -> new location.
+    """
+
+
+def migrate_logs(*files_or_directories: str) -> dict[str, str]:
+    """
+    Migrate files and directories relating to plugin logs to the recommended location and remove old locations.
+    Specified files will be migrated to `DECKY_PLUGIN_LOG_DIR`.
+    Specified directories will have their contents recursively migrated to `DECKY_PLUGIN_LOG_DIR`.
+
+    Returns the mapping of old -> new location.
+    """
+
+
+"""
+Logging
+"""
+
+logger: logging.Logger
+"""The main plugin logger writing to `DECKY_PLUGIN_LOG`."""
+
+"""
+Event handling
+"""
+# TODO better docstring im lazy
+async def emit(event: str, *args: Any) -> None:
+    """
+    Send an event to the frontend.
+    """