Fix welcome logo, real hex grid, Matrix boot messages, deeper TDS coverage

- WelcomePage: use official Lotus.png instead of generated SVG
- Hex Grid background: proper pointy-top hexagons via SVG data URI (was
  just triangles from linear-gradient trick)
- Boot sequence: Matrix-specific messages (TLS cert, E2EE Olm/Megolm,
  cross-signing, media proxy, /help hint)
- Terminal mode CSS: nav right border, header bottom glow, kbd TDS key
  style, abbr cyan underline, time amber color, img hover cyan outline,
  explicit body color anchor

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

src/app/pages/client/WelcomePage.tsx

@@ -1,7 +1,7 @@
 import React from 'react';
 import { Box, Button, Icon, Icons, Text, config, toRem } from 'folds';
 import { Page, PageHero, PageHeroSection } from '../../components/page';
-import CinnySVG from '../../../../public/res/svg/cinny.svg';
+import LotusLogo from '../../../../public/res/Lotus.png';
 
 export function WelcomePage() {
   return (
@@ -14,7 +14,7 @@ export function WelcomePage() {
       >
         <PageHeroSection>
           <PageHero
-            icon={<img width="70" height="70" src={CinnySVG} alt="Lotus Chat Logo" />}
+            icon={<img width="70" height="70" src={LotusLogo} alt="Lotus Chat" style={{ objectFit: "contain" }} />}
             title="Welcome to Lotus Chat"
             subTitle={
               <span>