fix(tauri): remove unused frontend shell-open authority

The main webview retained `shell:allow-open` even though the frontend never
uses the shell plugin directly. File-manager opening already flows through the
`open_game_files` command, which checks catalog membership and containment.

Remove only the frontend permission. The Rust shell plugin and dependency stay
available for the checked backend open operation and bundled unrar sidecar.

Test Plan:
- `just build-fixture` -- passed, including the frontend build and Tauri
  capability validation.
- `git diff --cached --check` -- passed.

crates/lanspread-tauri-deno-ts/src-tauri/capabilities/default.json

@@ -9,7 +9,6 @@
     "core:default",
     "core:window:allow-set-focus",
     "core:webview:allow-create-webview-window",
-    "shell:allow-open",
     "dialog:default",
     "store:default"
   ]