docs: mark Step 2.3 as complete in PLAN.md

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PLAN.md

@@ -67,18 +67,18 @@ Check off items as completed. Each phase builds on the previous.
 - [x] **Commit checkpoint** (29d5d3f)
 
 ### Step 2.3: Event Type Payloads
-- [ ] Create Pydantic models for all event payloads (spec §6):
-  - [ ] LocationCreated, LocationRenamed, LocationArchived
-  - [ ] AnimalCohortCreated, AnimalPromoted, AnimalMoved
-  - [ ] AnimalAttributesUpdated, AnimalTagged, AnimalTagEnded
-  - [ ] HatchRecorded, AnimalOutcome
-  - [ ] ProductCollected, ProductSold
-  - [ ] FeedPurchased, FeedGiven
-  - [ ] AnimalMerged, AnimalStatusCorrected
-- [ ] Create `events/validation.py` for payload validation
-- [ ] Implement tag normalization (spec §20)
-- [ ] Write tests for each payload model
-- [ ] **Commit checkpoint**
+- [x] Create Pydantic models for all event payloads (spec §6):
+  - [x] LocationCreated, LocationRenamed, LocationArchived
+  - [x] AnimalCohortCreated, AnimalPromoted, AnimalMoved
+  - [x] AnimalAttributesUpdated, AnimalTagged, AnimalTagEnded
+  - [x] HatchRecorded, AnimalOutcome
+  - [x] ProductCollected, ProductSold
+  - [x] FeedPurchased, FeedGiven
+  - [x] AnimalMerged, AnimalStatusCorrected
+- [x] Create `events/validation.py` for payload validation
+- [x] Implement tag normalization (spec §20)
+- [x] Write tests for each payload model
+- [x] **Commit checkpoint** (80784ff)
 
 ### Step 2.4: Projection Infrastructure
 - [ ] Create `projections/base.py` with Projection base class