feat(leads): sidecar polling service for auto-assigning unassigned leads

Replaces the untrusted platform function path (SDK's lead-auto-assign
was written but never deployed to either workspace — all leads created
after seeding are orphan).

Polls every 60s:
  1. Fetch up to 100 unassigned leads (assignedAgent empty or null)
  2. Fetch platform Agents whose live SupervisorService state is
     ready/calling/in-call/acw (skip offline/break/training/unknown)
  3. Build open-lead count per agent (single paginated query)
  4. Assign each unassigned lead to the least-loaded active agent —
     writes agent.name into lead.assignedAgent to match the worklist
     filter (assignedAgent: { eq: agentName })

Catches every lead-creation path: CSV import, enquiry form,
missed-call webhook, widget, livekit. No platform changes needed.

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

src/leads/leads.module.ts

@@ -0,0 +1,11 @@
+import { Module, forwardRef } from '@nestjs/common';
+import { PlatformModule } from '../platform/platform.module';
+import { SupervisorModule } from '../supervisor/supervisor.module';
+import { LeadAutoAssignService } from './lead-auto-assign.service';
+
+@Module({
+    imports: [PlatformModule, forwardRef(() => SupervisorModule)],
+    providers: [LeadAutoAssignService],
+    exports: [LeadAutoAssignService],
+})
+export class LeadsModule {}