Version the brand images' URLs, so a new mark reaches returning visitors

The logo, favicons and app icons are served from public/img under fixed
names with a browser cache of hours, and the service worker fetches them
through that cache. After the mark changed on 2026-09-27, returning
visitors kept the old cat until their copies expired, and the favicon
and an installed app's icon hold on longer still.

Every URL that names one now carries ?v=BRAND_V (src/lib/brand.ts,
brandImage()): the header, sign-in, About, the mail empty state, the
notification icons, index.html's favicon links, the manifest's icons
and the service worker's shell and notification icons. Date-stamped,
never a counter, for the sites' ASSET_V reason; the three static files
carry the value written out, and the comment says to keep them in step.

web/index.html

@@ -19,9 +19,9 @@
     <meta name="apple-mobile-web-app-capable" content="yes" />
     <meta name="apple-mobile-web-app-status-bar-style" content="default" />
     <meta name="mobile-web-app-capable" content="yes" />
-    <link rel="icon" href="/favicon.ico" sizes="any" />
-    <link rel="icon" type="image/png" sizes="64x64" href="/img/favicon-64.png" />
-    <link rel="apple-touch-icon" href="/img/apple-touch-icon.png" />
+    <link rel="icon" href="/favicon.ico?v=2026-09-27a" sizes="any" />
+    <link rel="icon" type="image/png" sizes="64x64" href="/img/favicon-64.png?v=2026-09-27a" />
+    <link rel="apple-touch-icon" href="/img/apple-touch-icon.png?v=2026-09-27a" />
     <link rel="manifest" href="/manifest.webmanifest" />
     <title>inbuxa</title>
   </head>