fix(themes): route remaining UI colours through theme tokens (#1014)

* fix(themes): route remaining UI colours through theme tokens

An audit found several surfaces still wired to the fixed Catppuccin
palette or hardcoded hex, so community themes could not recolour them:
the 5-star rating, the global search field, the gradient-text flourish,
badges and category-avatar text, and the What's New page + sidebar
banner. Rewire them to existing contract tokens — no new tokens, and the
built-in themes look identical (the values match). Community themes now
control these areas.

Also fixes device-sync rows referencing an undefined --bg-secondary
(they rendered with no background); they now use --bg-card.

* docs(themes): note the theme-coverage PR in the Theme Store entry

Add PR #1014 to the still-unreleased Theme Store changelog and credits
entry, alongside the other follow-ups.

src/styles/themes/utility-classes.css

@@ -1,6 +1,6 @@
 /* ─── Utility Classes ─── */
 .gradient-text {
-  background: linear-gradient(135deg, var(--ctp-mauve), var(--ctp-blue));
+  background: linear-gradient(135deg, var(--accent), var(--accent-2));
   -webkit-background-clip: text;
   -webkit-text-fill-color: transparent;
   background-clip: text;