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>

crates/punktfunk-host/Cargo.toml

@@ -179,6 +179,9 @@ windows-service = "0.7"
 # Read the GOG.com install registry (HKLM\SOFTWARE\WOW6432Node\GOG.com\Games) for the GOG store
 # provider — ergonomic + correct-by-construction vs. hand-rolled Reg* FFI for subkey enumeration.
 winreg = "0.56"
+# Parse each Xbox/Game-Pass game's MicrosoftGame.config (GDK manifest XML) for the Xbox store
+# provider — a small read-only DOM is all we need (Identity/Executable/ShellVisuals/StoreId).
+roxmltree = "0.21"
 # Software H.264 encoder (GPU-less path + NVENC fallback). The default `source` feature statically
 # compiles OpenH264 (BSD-2) — no system lib, builds on MSVC; nasm on PATH adds the SIMD fast path.
 openh264 = "0.9"