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/routes/settings.ts

@@ -16,6 +16,7 @@ function rowToLimits(row: typeof schema.instanceSettings.$inferSelect): Instance
     allowedFramerates: row.allowedFramerates.split(',').map(Number).filter((n) => VALID_FRAMERATES.includes(n)),
     maxResolution: row.maxResolution,
     maxFramerate: row.maxFramerate,
+    discoveryEnabled: row.discoveryEnabled === 1,
   };
 }
 
@@ -100,6 +101,10 @@ export async function settingsRoutes(app: FastifyInstance): Promise<void> {
       updateData.maxFramerate = body.maxFramerate;
     }
 
+    if (body.discoveryEnabled !== undefined) {
+      updateData.discoveryEnabled = body.discoveryEnabled ? 1 : 0;
+    }
+
     // Cross-field validation: min < max
     const currentRow = db.select().from(schema.instanceSettings).where(eq(schema.instanceSettings.id, 1)).get();
     if (!currentRow) {