Use a plain text note glyph for the music tab, not the emoji

Setting color explicitly wasn't enough: the 🎵 emoji has its own
baked-in colour (a muted grey-blue on at least one real platform) and
simply ignores the CSS color property, unlike a plain Unicode symbol.
Swapped to the bare eighth-note character (♪), which renders as text
and finally responds to the color already set on the button.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

web/src/lib/theme.ts

@@ -85,7 +85,10 @@ export const TAB_RAIL_CLEARANCE = 88;
  * smarthome tab only renders when Home Assistant is configured (see `App.tsx`); the
  * other two always show. */
 export const PAGE_ICON: Record<UiState["page"], string> = {
-  music: "🎵",
+  // A plain Unicode symbol, not the 🎵 emoji: that glyph's own built-in colour is a
+  // muted grey-blue on at least one real platform, which is illegible against the tab
+  // rail's own glass background and does not respond to `color` the way text does.
+  music: "♪",
   room: "💡",
   typing: "⌨️",
 };