Launcher: panel accounts via authlib-injector, skin & cape editor

Microsoft sign-in is gone. Server accounts now receive Yggdrasil tokens
from the panel and launch with authlib-injector pointed at the panel's
auth server, so online-mode servers verify players against it.

- Download authlib-injector from the panel mirror (fallback: official),
  SHA-256 verified and cached, with prefetched metadata
- New Skin & cape settings tab: upload, arm style, reset, cape picker
  with front/back previews
- Avatars render from the panel's head endpoint

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011ARcGWxLx21FwXJ3yfGriS

launcher/src-tauri/src/lib.rs

@@ -52,9 +52,11 @@ pub fn run() {
             commands::login_panel,
             commands::register_panel,
             commands::add_offline,
-            commands::ms_start,
-            commands::ms_finish,
-            commands::ms_cancel,
+            commands::account_profile,
+            commands::upload_skin,
+            commands::set_skin_model,
+            commands::delete_skin,
+            commands::set_cape,
             commands::select_account,
             commands::remove_account,
             commands::launch,