feat: Remind Me Later, mobile bookmarks, bug fixes, and doc cleanup

Features:
- Remind Me Later: message context menu item opens a preset time picker
  (20 min / 1 hr / 3 hr / tomorrow 9am); reminders persist to Matrix
  account data (io.lotus.reminders); ReminderMonitor fires a Lotus Toast
  when due, checks every 30s and on tab focus
- Mobile Bookmarks: BookmarksPanel now renders on all screen sizes;
  passes isMobile prop for full-screen absolute overlay on mobile

Bug fixes:
- usePan.ts: memory leak from stale closure in document listener cleanup
- EventReaders.tsx: replace hardcoded hex colors with TDS CSS variables
- CallControls.tsx: replace hardcoded hex colors with TDS CSS variables
- CustomHtml.css.ts: replace hardcoded yellow/black highlight with theme tokens

Docs:
- LOTUS_TODO.md: restore deleted content (Confirmed facts table, Pending
  Audits, P5-30 completed status, full feature descriptions), keep new
  additions (P4-7/8/9, P5-41–57, Implementation Reference), eliminate
  duplicate sections
- LOTUS_BUGS.md: merge RESILIENCE_AUDIT.md findings into Architectural &
  Resilience Audit table; delete RESILIENCE_AUDIT.md
- Remove stale LOTUS_DENOISE_ENGINEERING_REVIEW.md and LOTUS_TODO_REFERENCE.md

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

src/app/styles/CustomHtml.css.ts

@@ -117,7 +117,7 @@ export const CodeBlockBottomShadow = style({
   pointerEvents: 'none',
 
   height: config.space.S400,
-  background: `linear-gradient(to top, #00000022, #00000000)`,
+  background: `linear-gradient(to top, ${color.Surface.Container}22, transparent)`,
 });
 
 const BaseList = style({});
@@ -255,7 +255,7 @@ export const EmoticonImg = style([
 export const highlightText = style([
   DefaultReset,
   {
-    backgroundColor: 'yellow',
-    color: 'black',
+    backgroundColor: color.Warning.Container,
+    color: color.Warning.OnContainer,
   },
 ]);