refactor(settings): migrate to tile-preload + strict shims (Phase 3.11b-settings1)
Route peek://app/settings/settings.html through tile-preload by hardcoding a
trustedBuiltin capability grant in the window-open handler (ipc.ts), matching
the same pattern used for core glue windows (page-glue, etc.).
Migrate all 6 direct api.invoke() calls in app/settings/settings.js to the
strict tile-preload wrapper methods added in commit 70c7cfb4 (Phase 3.11b-shims):
- api.invoke('default-browser-status') -> api.app.getDefaultBrowserStatus()
- api.invoke('set-default-browser') -> api.app.setDefaultBrowser()
- api.invoke('backup-create') -> api.backup.create()
- api.invoke('backup-list') -> api.backup.list()
- api.invoke('backup-get-config') -> api.backup.getConfig()
- api.invoke('shell-open-path', ...) -> api.shell.openPath(...)
Legacy ipc.ts handlers for these channels are intentionally preserved: they
still serve app/diagnostic.html which has not yet been migrated.