feat(library): Windows Xbox / Game Pass store provider

XboxProvider scans each fixed drive's <drive>:\XboxGames for GDK games (presence of
Content\MicrosoftGame.config marks a game vs. an ordinary UWP app), parsing title /
Identity name / Executable Id / StoreId via roxmltree. The PackageFamilyName is READ
from the AppRepository\Packages\<PackageFullName> dir name (reduced to Name_Hash) —
never computed from the publisher. Launch via the AUMID (shell:AppsFolder\<PFN>!<AppId>)
through explorer in the interactive user session (UWP activation needs the user token,
which spawn_in_active_session already provides). Cover art (displaycatalog) is deferred
→ title-only. Known v1 gaps: custom .GamingRoot install folders + non-GDK pure-UWP Store
games (under the ACL-locked WindowsApps) aren't enumerated.

New windows_launch_for `aumid` arm; XboxProvider wired into all_games() under cfg(windows).
Dep: roxmltree (Windows). Windows unit tests cover MicrosoftGame.config parsing (incl. the
ms-resource title fallback), the PackageFullName→PFN reduction, and the aumid launch.

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

Cargo.lock

@@ -2728,6 +2728,7 @@ dependencies = [
  "rand 0.8.6",
  "rcgen",
  "reis",
+ "roxmltree",
  "rsa",
  "rusqlite",
  "rustls",
@@ -3055,6 +3056,15 @@ dependencies = [
  "windows-sys 0.52.0",
 ]
 
+[[package]]
+name = "roxmltree"
+version = "0.21.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f1964b10c76125c36f8afe190065a4bf9a87bf324842c05701330bba9f1cacbb"
+dependencies = [
+ "memchr",
+]
+
 [[package]]
 name = "rpkg-config"
 version = "0.1.2"