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/src/lib/branding.ts

@@ -1,12 +1,10 @@
 declare global {
   interface Window {
-    __MINSTREL__?: { appName: string; description: string };
+    __MINSTREL__?: { appName: string };
   }
 }
 
 const DEFAULT_APP_NAME = 'Minstrel';
-const DEFAULT_DESCRIPTION =
-  'Self-hosted music server with Subsonic compatibility, smart shuffle, and Lidarr integration.';
 
 const isRenderedToken = (v: string | undefined): v is string =>
   typeof v === 'string' && v.length > 0 && !v.includes('{{');
@@ -18,13 +16,6 @@ export const appName = (): string => {
     : DEFAULT_APP_NAME;
 };
 
-export const description = (): string => {
-  if (typeof window === 'undefined') return DEFAULT_DESCRIPTION;
-  return isRenderedToken(window.__MINSTREL__?.description)
-    ? window.__MINSTREL__!.description
-    : DEFAULT_DESCRIPTION;
-};
-
 export const pageTitle = (section?: string): string =>
   section ? `${appName()} · ${section}` : appName();