Phase 2 scaffold: mitra online status & pairing logic

Add mitra online/offline status with heartbeat-based auto-offline,
customer-mitra pairing via Valkey pub/sub blast, session management,
and control center dashboard with real-time stats.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/src/routes/internal/config.routes.js

@@ -1,6 +1,6 @@
 import { authenticate, requirePermission } from '../../plugins/auth.js'
 import { getCcUserByFirebaseUid } from '../../services/cc-user.service.js'
-import { getAnonymityConfig, setAnonymityConfig } from '../../services/config.service.js'
+import { getAnonymityConfig, setAnonymityConfig, getMaxCustomersPerMitra, setMaxCustomersPerMitra } from '../../services/config.service.js'
 
 const attachCcUser = async (request, reply) => {
   const user = await getCcUserByFirebaseUid(request.firebaseUser.uid)
@@ -26,4 +26,22 @@ export const internalConfigRoutes = async (app) => {
     const config = await setAnonymityConfig(anonymity_enabled)
     return reply.send({ success: true, data: config })
   })
+
+  app.get('/max-customers-per-mitra', {
+    preHandler: [authenticate, attachCcUser, requirePermission('config', 'read')],
+  }, async (request, reply) => {
+    const config = await getMaxCustomersPerMitra()
+    return reply.send({ success: true, data: config })
+  })
+
+  app.patch('/max-customers-per-mitra', {
+    preHandler: [authenticate, attachCcUser, requirePermission('config', 'update')],
+  }, async (request, reply) => {
+    const { max_customers_per_mitra } = request.body ?? {}
+    if (typeof max_customers_per_mitra !== 'number' || max_customers_per_mitra < 1) {
+      return reply.code(422).send({ success: false, error: { code: 'VALIDATION_ERROR', message: 'max_customers_per_mitra must be a positive number' } })
+    }
+    const config = await setMaxCustomersPerMitra(max_customers_per_mitra)
+    return reply.send({ success: true, data: config })
+  })
 }