chore(web): post-#363 cleanup — DRY tripwires, drop unused description, singular playlist title

M2 — Add TODO(#375) tripwire comments where the dark/light theme-color
hex pair is duplicated outside tokens.json (vite.config.ts and
applyMetaThemeColor.svelte.ts). Refactoring is out of scope for #363;
the comments are stop signs for the next person who edits these.

M5 — The SPA never reads window.__MINSTREL__.description. The OG meta
description is server-rendered and complete on its own. Drop the dead
inline-script field and the corresponding helpers in branding.ts.
Server-side BrandingConfig.Description stays — it's still used for
<meta name="description"> and og:description.

Copy nit — Playlist detail page title becomes "Playlist · Foo"
matching the singular form already used by Artist · / Album ·.

web/vite.config.ts

@@ -29,9 +29,10 @@ const injectGoTokensPlugin = {
     <meta property="og:image" content="/brand/og-image.png">
     <meta property="og:type" content="website">
     <meta name="twitter:card" content="summary_large_image">
+    <!-- TODO(#375): keep theme-color hex in sync with tokens.json colors.dark.obsidian / colors.light.obsidian -->
     <meta name="theme-color" media="(prefers-color-scheme: dark)" content="#14171A">
     <meta name="theme-color" media="(prefers-color-scheme: light)" content="#F8F5EE">
-    <script>window.__MINSTREL__ = { appName: "{{ .AppName }}", description: "{{ .Description }}" };</script>`;
+    <script>window.__MINSTREL__ = { appName: "{{ .AppName }}" };</script>`;
 
     // Fail loudly if either anchor drifts. A silent .replace() no-op
     // would ship a build with un-substituted Go template tokens missing,