Rebrand as Playlink with a new sunset theme

- Name: Playlink in the UI, page title, footer, messages and README
  (file names like playlink.db and .playlink-trash are unchanged).
- Theme: plum-black surfaces with a coral-to-pink accent, a soft glow
  behind the page, gradient primary buttons, toggles and progress bars,
  accent focus rings and slim scrollbars.
- New logo (beamed notes on the brand gradient) and a Play/link wordmark.
- Inter variable font, bundled so it works under the strict CSP.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/index.html

@@ -4,7 +4,8 @@
     <meta charset="UTF-8" />
     <meta name="viewport" content="width=device-width, initial-scale=1.0" />
     <link rel="icon" href="/favicon.svg" type="image/svg+xml" />
-    <title>playlink</title>
+    <title>Playlink</title>
+    <meta name="theme-color" content="#0d0b12" />
   </head>
   <body>
     <div id="root"></div>