feat(changelog): replace auto-modal with sidebar banner + /whats-new page

Removes the giant startup changelog modal. After an update, a compact
neutral-palette pill now sits above Now Playing in the sidebar saying
"Changelog — vX.Y.Z". Clicking opens a proper /whats-new page in the
main content area; X dismisses. Page renders the current version's
CHANGELOG entry with inline Markdown (headings, lists, blockquotes,
hr, bold/italic/code, and real [label](url) links that open via the
Tauri shell plugin).

Visual tokens are hardcoded slate/gray/blue so the banner and page look
identical across every theme (dark, light, skeuomorphic, whatever) —
requested for consistent contrast. Auto-mark-as-seen removed from the
page; the banner only goes away on explicit dismiss, so users can
re-read as often as they want.

Settings → About gains a "Release notes" row with a link that resets
the seen-version and opens the page, so the banner can be retriggered
manually (also helpful for dev builds ahead of the current tag).

The existing "Show changelog on update" toggle now gates the banner
instead of the modal; description strings updated in all 8 locales.

fix(themes): WCAG contrast audit — mocha + winmedplayer + wista

Mocha (Catppuccin dark)
  .track-size used --ctp-overlay0 directly (3.36:1 on bg-app, 2.57
  on bg-card). Swapped to --text-muted → 7.37 / 5.65. Fix also lifts
  macchiato/frappe/latte which shared the failure.

WinMedPlayer (Luna)
  --text-muted #b8d0f8 (3.87:1 on bg-app) → #e8f0ff (5.28)
  --border   #2a5090 (1.31 on bg-app)   → #071027 (3.12, meets 3:1 UI)

Wista (Vista Aero)
  Lyrics pane sits on bg-sidebar #0e1e3e but used --text-primary
  (#0d1d3c) for active lines — 1.01:1, literally invisible. Added
  component overrides: .lyrics-line / .lyrics-status / word-synced
  variants → #aac8f0 (9.60), .lyrics-line.active → #ffffff (16.48).
  Palette: --warning #c8980c → #735a00 (2.37 → 5.91 on bg-app),
  --text-muted #4870a8 → #3f6aa0 (4.23 → 4.65 on bg-card).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/locales/en.ts

@@ -601,11 +601,13 @@ export const enTranslation = {
     aboutVersion: 'Version',
     aboutBuiltWith: 'Built with Tauri · React · TypeScript · Rust/rodio',
     aboutAiCredit: 'Developed with the support of Claude Code by Anthropic',
+    aboutReleaseNotesLabel: 'Release notes',
+    aboutReleaseNotesLink: "Open this version's what's-new",
     aboutContributorsLabel: 'Contributors',
     aboutSpecialThanksLabel: 'Special Thanks',
     changelog: 'Changelog',
     showChangelogOnUpdate: "Show 'What's New' on update",
-    showChangelogOnUpdateDesc: "Automatically show what's new when a new version is launched for the first time.",
+    showChangelogOnUpdateDesc: "Show a discreet changelog banner above Now Playing after an update. Click opens the release notes; X dismisses it.",
     randomMixTitle: 'Random Mix',
     randomMixBlacklistTitle: 'Custom Filter Keywords',
     randomMixBlacklistDesc: 'Songs are excluded when any keyword matches their genre, title, album, or artist (active when the checkbox above is on).',
@@ -741,6 +743,14 @@ export const enTranslation = {
     dontShowAgain: "Don't show again",
     close: 'Got it',
   },
+  whatsNew: {
+    title: "What's New",
+    empty: 'No changelog entry for this version yet.',
+    bannerTitle: 'Changelog',
+    bannerCollapsed: "What's new in v{{version}}",
+    dismiss: 'Dismiss',
+    close: 'Close',
+  },
   help: {
     title: 'Help',
     s1: 'Getting Started',