polish(web): favicon, Punktfunk casing, display-save toast, idle stop button

- Favicon: the brand-mark lens SVG at /favicon.svg, linked from the root head.
- Branding: user-facing "punktfunk" → "Punktfunk" (tab title, app_name,
  pairing prose, the logo aria-labels/SVG titles) — protocol identifiers
  (punktfunk/1, _punktfunk._udp, binary/module names) stay lowercase.
- The display policy auto-saves on every preset pick / field edit with no
  signal; mount @unom/ui's sonner Toaster in the root and fire a success toast
  from the save funnel's onSuccess (new i18n key, en + de). First toast usage
  in the console — errors stay inline as before.
- The stop-session button rendered destructive-red even with nothing to stop:
  variant switches to the muted `secondary` while no session is active.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

web/src/sections/Dashboard/view.tsx

@@ -78,7 +78,7 @@ export const DashboardView: FC<{
 											{m.action_request_idr()}
 										</Button>
 										<Button
-											variant="destructive"
+											variant={s.session ? "destructive" : "secondary"}
 											size="sm"
 											disabled={!s.session || isStopping}
 											onClick={onStopSession}