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/es.ts

@@ -592,11 +592,13 @@ export const esTranslation = {
     aboutVersion: 'Versión',
     aboutBuiltWith: 'Construido con Tauri · React · TypeScript · Rust/rodio',
     aboutAiCredit: 'Desarrollado con el apoyo de Claude Code by Anthropic',
+    aboutReleaseNotesLabel: 'Notas de la versión',
+    aboutReleaseNotesLink: 'Abrir las novedades de esta versión',
     aboutContributorsLabel: 'Contribuidores',
     aboutSpecialThanksLabel: 'Agradecimientos Especiales',
     changelog: 'Registro de Cambios',
     showChangelogOnUpdate: "Mostrar 'Novedades' al actualizar",
-    showChangelogOnUpdateDesc: "Muestra automáticamente las novedades cuando se lanza una nueva versión por primera vez.",
+    showChangelogOnUpdateDesc: 'Muestra un discreto banner de changelog encima de Now Playing tras una actualización. Clic abre las notas de la versión; X lo oculta.',
     randomMixTitle: 'Mezcla Aleatoria',
     randomMixBlacklistTitle: 'Palabras Clave de Filtro Personalizadas',
     randomMixBlacklistDesc: 'Las canciones se excluyen cuando cualquier palabra clave coincide con su género, título, álbum o artista (activo cuando el checkbox de arriba está activado).',
@@ -732,6 +734,14 @@ export const esTranslation = {
     dontShowAgain: 'No mostrar de nuevo',
     close: 'Entendido',
   },
+  whatsNew: {
+    title: 'Novedades',
+    empty: 'Aún no hay entrada de changelog para esta versión.',
+    bannerTitle: 'Changelog',
+    bannerCollapsed: 'Novedades en v{{version}}',
+    dismiss: 'Ocultar',
+    close: 'Cerrar',
+  },
   help: {
     title: 'Ayuda',
     s1: 'Primeros Pasos',