fix: DM avatar color and reactions in federation + explore/server discovery

- Fix DM welcome header avatar using home identity for correct gradient color
- Register DM channel IDs in channelOriginMap so federated DM operations
  (reactions, messages, typing) route to the correct instance
- Pass origin when creating DM channels from friends list and WS events
- Add server discovery/explore page with public server listings
- Add server visibility and description fields

packages/server/src/index.ts

@@ -19,6 +19,7 @@ import { socialRoutes } from './routes/social.js';
 import { settingsRoutes } from './routes/settings.js';
 import { utilRoutes } from './routes/utils.js';
 import { instanceRoutes } from './routes/instance.js';
+import { exploreRoutes } from './routes/explore.js';
 import { registerWebSocket } from './ws/handler.js';
 import path from 'path';
 import fs from 'fs';
@@ -77,6 +78,7 @@ async function main(): Promise<void> {
   await app.register(settingsRoutes);
   await app.register(utilRoutes);
   await app.register(instanceRoutes);
+  await app.register(exploreRoutes);
   await app.register(registerWebSocket);
 
   app.get('/api/health', async () => {