feat: Add presence heartbeat for Matrix online status

- matrix-gateway: POST /internal/matrix/presence/online endpoint
- usePresenceHeartbeat hook with activity tracking
- Auto away after 5 min inactivity
- Offline on page close/visibility change
- Integrated in MatrixChatRoom component

backend/http/platforms.routes.ts

@@ -0,0 +1,48 @@
+/**
+ * Platforms Routes
+ * Based on: api-mvp.md
+ * 
+ * Endpoints:
+ * - POST /api/v1/platforms - Create platform
+ * - GET /api/v1/platforms - List platforms
+ */
+
+import { Router } from 'express';
+import { daoFactoryService } from '../../services/dao-factory/dao-factory.service';
+import { registryService } from '../../services/registry/registry.service';
+import type { CreatePlatformInput } from '../../domain/dao/types';
+
+export const platformsRoutes = Router();
+
+// POST /api/v1/platforms - Create platform
+platformsRoutes.post('/', async (req, res) => {
+  try {
+    const userId = (req as any).userId;
+    const input: CreatePlatformInput = req.body;
+    
+    const result = await daoFactoryService.createPlatform(userId, input);
+    
+    res.status(201).json(result);
+  } catch (error: any) {
+    res.status(400).json({
+      error: error.message || 'BAD_REQUEST',
+      message: error.message,
+    });
+  }
+});
+
+// GET /api/v1/platforms - List platforms
+platformsRoutes.get('/', async (req, res) => {
+  try {
+    const platforms = await registryService.listPlatforms();
+    
+    res.json({ items: platforms });
+  } catch (error: any) {
+    res.status(500).json({
+      error: 'INTERNAL_ERROR',
+      message: error.message,
+    });
+  }
+});
+
+