fix: improve accessibility and tokenize remaining hardcoded CSS values

- FAB focus ring: double-ring pattern replacing invisible #fff outline
- forced-colors media query for Windows High Contrast Mode
- New tokens: --color-accent-secondary, --content-max-width-narrow, --cal-hour-height
- Apple sync logo uses semantic tokens for correct dark mode inversion
- Sidebar logo gradient references token instead of hardcoded #7C5CFC

public/styles/settings.css

@@ -14,7 +14,7 @@
    -------------------------------------------------------- */
 
 .settings-page {
-  max-width: 720px;
+  max-width: var(--content-max-width-narrow);
   margin: 0 auto;
 }
 
@@ -250,8 +250,8 @@
 }
 
 .settings-sync-logo--apple {
-  background: var(--neutral-900);
-  color: var(--neutral-50);
+  background: var(--color-text-primary);
+  color: var(--color-bg);
 }
 
 .settings-sync-info__name {