fix: presence MaxListeners leak + self-host fonts to fix tracking prevention

Presence: subscribe on MatrixClient (mx) instead of individual User objects.
User EventEmitters have a 10-listener default; the same user appears in many
mounted components simultaneously (member list, avatars, presence rings) and
was accumulating 11+ listeners per event, causing MaxListenersExceededWarning
on User.presence, User.currentlyActive, and User.lastPresenceTs.

Fonts: download JetBrains Mono and Fira Code latin subsets to public/fonts/
and replace Google Fonts CDN links (two external origins) with a local CSS
file. Windows WebView2 tracking prevention was blocking googleapis.com and
gstatic.com, logging 18+ "blocked" warnings per session. VT323 remains on
Google Fonts as it's decorative and not a default option.

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

index.html

@@ -30,9 +30,10 @@
     <link rel="preconnect" href="https://fonts.googleapis.com" crossorigin />
     <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin />
     <link
-      href="https://fonts.googleapis.com/css2?family=Fira+Code:wght@400;500;600&family=JetBrains+Mono:ital,wght@0,400;0,600;0,700;1,400&family=VT323&display=swap"
+      href="https://fonts.googleapis.com/css2?family=VT323&display=swap"
       rel="stylesheet"
     />
+    <link rel="stylesheet" href="/fonts/custom-fonts.css" />
     <link id="favicon" rel="shortcut icon" href="./public/favicon.ico" />
 
     <link rel="manifest" href="/manifest.json" />