feat(models): Add priority field to Ticket dataclass and update serialization

conductor/tracks/ticket_queue_mgmt_20260306/plan.md

@@ -5,10 +5,10 @@
 ## Phase 1: Priority Field
 Focus: Add priority to Ticket model
 
-- [ ] Task 1.1: Initialize MMA Environment
+- [x] Task 1.1: Initialize MMA Environment
     - Run `activate_skill mma-orchestrator` before starting
 
-- [ ] Task 1.2: Add priority field to Ticket
+- [~] Task 1.2: Add priority field to Ticket
     - WHERE: `src/models.py` `Ticket` dataclass
     - WHAT: Add `priority: str = "medium"` field
     - HOW: