feat: complete phase 2 -- multi-agent routing, interrupt TTL, escalation, templates

- Intent classification with LLM structured output (single/multi/ambiguous)
- Discount agent with apply_discount and generate_coupon tools
- Interrupt manager with 30-min TTL auto-expiration and retry prompts
- Webhook escalation module with exponential backoff retry (max 3)
- Three vertical industry templates (e-commerce, SaaS, fintech)
- Template loading in AgentRegistry
- Enhanced supervisor prompt with dynamic agent descriptions
- 153 tests passing, 90.18% coverage

backend/agents.yaml

@@ -20,6 +20,17 @@ agents:
     tools:
       - cancel_order
 
+  - name: discount
+    description: "Applies discounts and generates coupon codes. Use when the customer asks for discounts, promotions, or coupon codes."
+    permission: write
+    personality:
+      tone: "generous and accommodating"
+      greeting: "I can help you with discounts and coupons!"
+      escalation_message: "Let me connect you with our promotions team."
+    tools:
+      - apply_discount
+      - generate_coupon
+
   - name: fallback
     description: "Handles general questions, unclear requests, and conversations that don't match other agents."
     permission: read