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/components/brand-mark.tsx

@@ -5,13 +5,13 @@
 export function BrandMark({ className }: { className?: string }) {
 	return (
 		<svg
-			aria-label="punktfunk"
+			aria-label="Punktfunk"
 			role="img"
 			xmlns="http://www.w3.org/2000/svg"
 			viewBox="0 0 1000 1000"
 			className={className}
 		>
-			<title>punktfunk</title>
+			<title>Punktfunk</title>
 			<path
 				d="M403.037,791.672c107.586,0 194.41,-86.824 194.41,-194.41c0,-107.586 -86.824,-194.41 -194.41,-194.41c-107.586,0 -194.41,86.824 -194.41,194.41c0,107.586 86.824,194.41 194.41,194.41Z"
 				fill="#a79ff8"