Fold thirty-one settings pages into fifteen categories with tabs

The sidebar was a flat scan of thirty-one rows; now it reads like a
settings app. Multi-subject categories (Input, Network & Sharing,
Applications, Users & Accounts, Privacy & Security, System) carry an
Appearance-style tab strip above the page, drawn by the shell so the
leaf pages themselves are untouched. The taxonomy lives in one new
file, services/SettingsRoutes.qml; the sidebar, the strip, route
validation, search breadcrumbs, and both generators derive from it.

ShellState.settingsPage still holds leaf ids, so every deep link, IPC
call, and search result keeps working — and now lands on the exact
tab. Dictation moves out of Sound onto its own page under Input, with
a handoff back to Sound for the microphone. The strip scrolls when
System's nine tabs outgrow a tiled window. All 161 contracts pass.

Claude-Session: https://claude.ai/code/session_01Ms2FbjQy31TVf3CEvQhGM8

config/dot/quickshell/services/ShellState.qml

@@ -118,8 +118,10 @@ Singleton {
     }
 
     function showSettings(page: string): void {
-        const allowed = ["home", "appearance", "displays", "connectivity", "home-phone", "desktop", "sound", "gaming", "notifications", "screen-intelligence", "shortcuts", "mouse", "privacy", "region", "accounts", "accessibility", "power", "datetime", "applications", "updates", "storage", "snapshots", "users", "sharing", "firewall", "printers", "containers", "ssh-keys", "services", "manual", "about"];
-        root.settingsPage = allowed.indexOf(page) >= 0 ? page : "home";
+        // SettingsRoutes owns the route table: a leaf id passes through, a
+        // category id lands on its first available tab, and anything unknown
+        // redirects to home rather than rendering a blank loader.
+        root.settingsPage = SettingsRoutes.resolve(page);
         DesktopPreferences.set("lastPage", root.settingsPage);
         root.settingsOpen = true;
     }