Name the icons by their contents in the pages (#57)

/favicon.png, /apple-touch-icon.png and /logo.svg are kept a day under
fixed names, so after the new logo went out, curl through the tunnel and
browsers still got the old one. The pages now ask for them as
/favicon.png?v=<hash>, the way they already ask for app.js and app.css,
so a changed icon is a new URL for every cache on the way. /favicon.ico
cannot carry a query, as browsers ask for it on their own; it keeps the
day.

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

web/build.mjs

@@ -72,6 +72,11 @@ export function buildPage(name, { minify = true } = {}) {
   let out = page.replace(marker, `<script src="/${script}?v=${hash(js)}"></script>`);
   out = out.replace(/<link rel="stylesheet" data-src="[^"]*">/,
     () => `<link rel="stylesheet" href="/${STYLE}?v=${hash(buildStyle({ minify }))}">`);
+  // 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)="\/(favicon\.png|apple-touch-icon\.png|logo\.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 });
   const bad = (r.errors || []).filter(e => e.level === 'Error');