feat: add health alerts field and delete actions for pets and clients

- Add health_alerts column to pets table (migration 0001)
- Update DB schema, shared types, and API Zod validation
- Show health alerts prominently (red badge) in pet cards
- Add health alerts field to pet form with allergy/condition placeholder
- Add delete button per pet with confirmation dialog
- Add delete client button with cascade warning

Closes groombook/groombook#2

Co-Authored-By: Paperclip <noreply@paperclip.ing>

packages/db/migrations/0001_pet_health_alerts.sql

@@ -0,0 +1 @@
+ALTER TABLE "pets" ADD COLUMN "health_alerts" text;