Add typecheck + CI checks, light theme with self-hosted Inter, fix real-model test

- Typecheck: typescript 7 devDependency, `bun run typecheck`; CI gains a
  `check` stage (install, typecheck, fast tests) gating image builds (D-038).
- Light theme: every colour is a token; prefers-color-scheme: light
  overrides them. Inter Variable self-hosted from @fontsource-variable/inter,
  kept out of Bun's CSS inlining and precached (scripts/fonts.ts, D-037).
  Backend select no longer overflows on narrow phones.
- tests/live-real-model.test.ts: time budget scales with clip length and
  en_alien gets a measured WER bar; it had failed since July (D-039).
- Delete the temporary isolate_wer2.ts; fix icon "not checked in" comments
  and the README's model-weights location.
- Agent docs: branch naming, typecheck, CI, Bun CSS gotcha, permissions.

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

src/index.html

@@ -12,7 +12,8 @@
          The manifest's own icon URLs stay at the fixed /icons/ paths, which
          src/index.ts (dev) and scripts/build.ts (production) serve. -->
     <link rel="manifest" href="./pwa/manifest.webmanifest" />
-    <meta name="theme-color" content="#16181d" />
+    <meta name="theme-color" content="#16181d" media="(prefers-color-scheme: dark)" />
+    <meta name="theme-color" content="#f5f6f8" media="(prefers-color-scheme: light)" />
     <link rel="apple-touch-icon" href="./pwa/icons/icon-192.png" />
     <title>Whisper Web — on-device speech-to-text</title>
   </head>