The tab's icon follows light and dark mode (#64)

The logo on the page switched with the mode (#63), but the tab's icon
was always favicon.png, the light logo. web/favicon-dark.png is
logo-dark.svg at 128px, served beside it, and the theme script points
the icon link at whichever matches data-mode, so it follows the theme
the account chose, not only the system. The sign-in page, with no
account, picks by the system's with two media-bound links.
/favicon.ico, which a browser asks for on its own, stays the light one.

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

web/admin.html

@@ -5,7 +5,7 @@
 <meta name="viewport" content="width=device-width, initial-scale=1">
 <meta name="color-scheme" content="dark light">
 <title>iPX admin</title>
-<link rel="icon" type="image/png" sizes="128x128" href="/favicon.png">
+<link rel="icon" type="image/png" sizes="128x128" id="favicon" href="/favicon.png" data-light="/favicon.png" data-dark="/favicon-dark.png">
 <link rel="apple-touch-icon" href="/apple-touch-icon.png">
 <link rel="stylesheet" data-src="app.css">
 </head>

web/build.mjs

@@ -75,7 +75,7 @@ export function buildPage(name, { minify = true } = {}) {
   // The icons are named by their contents too. They are kept a day under a fixed name, and a new
   // logo went unseen for that day, in browsers and at Cloudflare's edge. The server ignores the
   // query; /favicon.ico, which a browser asks for on its own, cannot carry one.
-  out = out.replace(/(href|src|srcset)="\/(favicon\.png|apple-touch-icon\.png|logo\.svg|logo-dark\.svg)"/g,
+  out = out.replace(/(href|src|srcset|data-light|data-dark)="\/(favicon\.png|favicon-dark\.png|apple-touch-icon\.png|logo\.svg|logo-dark\.svg)"/g,
     (_, attr, file) => `${attr}="/${file}?v=${hash(fs.readFileSync(path.join(here, file)))}"`);
   if (!minify) return { html: out, js, script };
   const r = html.minifySync(out, { minifyJs: false, minifyCss: true, removeComments: true });

web/index.html

@@ -5,7 +5,7 @@
 <meta name="viewport" content="width=device-width, initial-scale=1, viewport-fit=cover">
 <meta name="color-scheme" content="dark light">
 <title>iPX</title>
-<link rel="icon" type="image/png" sizes="128x128" href="/favicon.png">
+<link rel="icon" type="image/png" sizes="128x128" id="favicon" href="/favicon.png" data-light="/favicon.png" data-dark="/favicon-dark.png">
 <link rel="apple-touch-icon" href="/apple-touch-icon.png">
 <link rel="stylesheet" data-src="app.css">
 </head>

web/login.html

@@ -4,7 +4,8 @@
 <meta name="viewport" content="width=device-width, initial-scale=1">
 <meta name="color-scheme" content="dark light">
 <title>Sign in — iPX</title>
-<link rel="icon" type="image/png" sizes="128x128" href="/favicon.png">
+<link rel="icon" type="image/png" sizes="128x128" href="/favicon.png" media="(prefers-color-scheme:light)">
+<link rel="icon" type="image/png" sizes="128x128" href="/favicon-dark.png" media="(prefers-color-scheme:dark)">
 <link rel="apple-touch-icon" href="/apple-touch-icon.png">
 <style>
 /* Inter, from ipx itself; see the same rule in index.html. */

web/src/theme.ts

@@ -35,6 +35,8 @@ function setTheme(name = theme.name, mode = theme.mode, save = false){
   // A theme with one palette has it whatever the mode; both of those are light.
   root.dataset.mode = !both ? 'light'
     : theme.mode === 'auto' ? (systemDark && !systemDark.matches ? 'light' : 'dark') : theme.mode;
+  // The tab's icon in the same variant as the logo on the page.
+  const fav = $('#favicon'); if(fav) fav.href = fav.dataset[root.dataset.mode];
   const sel = $('#stheme'); if(sel) sel.value = theme.name;
   const ms = $('#smode'); if(ms) ms.value = theme.mode;
   const mf = $('#smodefield'); if(mf) mf.hidden = !both;