fix: add favicon (SVG + PNG + ICO), fix static MIME types (#613)

Squash-merges PR #613. Adds favicon to the app (was missing entirely — blank tab icon). 1371 tests passing, QA harness green. Review by independent agent (see PR comments). Follow-up commit addresses all three reviewer notes: hoisted _STATIC_MIME to module scope, fixed charset=utf-8 being appended to binary MIME types, confirmed correct MIME types on all three favicon formats.

Co-authored-by: tiansiyuan <tiansiyuan@users.noreply.github.com>

static/index.html

@@ -4,6 +4,9 @@
 <meta charset="utf-8">
 <meta name="viewport" content="width=device-width, initial-scale=1">
 <title>Hermes</title>
+<link rel="icon" type="image/svg+xml" href="static/favicon.svg">
+<link rel="icon" type="image/png" sizes="32x32" href="static/favicon-32.png">
+<link rel="shortcut icon" href="static/favicon.ico">
 <!-- base href enables subpath mount support; all static paths must stay relative (no leading slash) -->
 <script>(function(){var p=location.pathname.endsWith('/')?location.pathname:(location.pathname.replace(/\/[^\/]*$/,'/')||'/');document.write('<base href="'+location.origin+p+'">');})()</script>
 <script>(function(){var t=localStorage.getItem('hermes-theme');if(t==='system'){t=window.matchMedia('(prefers-color-scheme:dark)').matches?'dark':'light';}if(t&&t!=='dark')document.documentElement.dataset.theme=t;})()</script>