Sideload Linux and Windows builds as Steam Devkit Games

Dropping a game's .zip, folder or .exe on Send to Frame now adds it to the
headset's Steam library through Valve's SteamOS Devkit title path, with the
runtime picked from the program's header: Windows PE -> Proton Experimental
(steam_play=1), aarch64 ELF -> SteamLinuxRuntime_4-arm64, x86-64 ELF ->
SteamLinuxRuntime_4 (through FEX). Other architectures are refused.

- frame/devkit-utils: Valve's devkit-utils vendored unmodified (MIT,
  steamos-devkit v0.20260925.1), synced to ~/devkit-utils by stamp, bundled in
  the app and compiled in CI.
- ui/frame_titles.py: inspect (safe unzip, ELF/PE classification, launch
  target ranking), install(path, name=None, exe=None, runtime=None,
  progress=None), list, launch, remove, plus a CLI.
- ui/server.py: /api/titles (inspect/install/discard/launch/remove),
  /api/titles/job progress, and an upload mode 'title'.
- ui/index.html: confirm dialog (name, launch target, runtime), install
  progress, and a Sideloaded titles list with Launch and Remove. The app's
  preload passes a dropped folder's path.
- tests and docs/sideloading.md. Device-side behaviour is inferred from
  Valve's source; the headset was offline, so none of it has been checked on
  a Frame yet.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

frame/devkit-utils/steamos-list-games

@@ -0,0 +1,34 @@
+#!/usr/bin/env python3
+
+import os
+import logging
+import argparse
+import getpass
+import json
+from subprocess import DEVNULL
+
+logging.basicConfig(format='%(message)s', level=logging.DEBUG)
+logger = logging.getLogger(__name__)
+
+DEVKIT_TOOL_FOLDER = os.path.expanduser('~/devkit-game')
+
+if __name__ == '__main__':
+    parser = argparse.ArgumentParser()
+    parser.add_argument('--verbose', required=False, action='store_true')
+    conf = parser.parse_args()
+
+    if conf.verbose:
+        logger.setLevel(logging.DEBUG)
+    else:
+        logger.setLevel(logging.INFO)
+
+    ret = []
+    if os.path.isdir(DEVKIT_TOOL_FOLDER):
+        for filename in os.listdir(DEVKIT_TOOL_FOLDER):
+            gamefolder = os.path.join(DEVKIT_TOOL_FOLDER, filename)
+            if os.path.isdir(gamefolder):
+                ret.append( {
+                    'gameid': filename,
+                } )
+
+    print(json.dumps(ret))