feat: P5-21 mention color, P5-22 font selector, P5-27 notification presets; update docs

- P5-21: Custom @mention highlight color picker in Settings → Appearance.
  CSS vars with luminance-computed text color; resets cleanly to theme default.
- P5-22: Font selector (System, Inter, JetBrains Mono, Fira Code) in
  Settings → Appearance. Fira Code added to Google Fonts preload.
- P5-27: Gaming/Work/Sleep preset buttons at top of Settings → Notifications.
  Each atomically applies a group of notification settings.
- AppearanceEffects component in App.tsx applies CSS vars on settings change.
- LOTUS_BUGS.md: mark presence + manifest icon bugs as resolved.
- LOTUS_TODO.md: mark P3-6, P5-21, P5-22, P5-27 as [x].
- LOTUS_FEATURES.md: document all four completed features.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/styles/CustomHtml.css.ts

@@ -169,9 +169,9 @@ export const Mention = recipe({
   variants: {
     highlight: {
       true: {
-        backgroundColor: color.Success.Container,
-        color: color.Success.OnContainer,
-        boxShadow: `0 0 0 ${config.borderWidth.B300} ${color.Success.ContainerLine}`,
+        backgroundColor: `var(--mention-highlight-bg, ${color.Success.Container as string})`,
+        color: `var(--mention-highlight-text, ${color.Success.OnContainer as string})`,
+        boxShadow: `0 0 0 ${config.borderWidth.B300} var(--mention-highlight-border, ${color.Success.ContainerLine as string})`,
       },
     },
     focus: {