docs: mark Step 4.4 as complete in PLAN.md

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PLAN.md

@@ -169,15 +169,14 @@ Check off items as completed. Each phase builds on the previous.
 - [x] **Commit checkpoint** (d53decd)
 
 ### Step 4.4: 30-Day Stats Computation
-- [ ] Create migration for egg_stats_30d_by_location table
-- [ ] Create `projections/stats.py` with EggStatsProjection
-- [ ] Implement bird-days calculation from intervals
-- [ ] Implement layer-eligible days filtering
-- [ ] Implement feed proration formula
-- [ ] Implement cost calculations (integer cents)
-- [ ] Create `services/stats.py` with get_egg_stats (compute on read)
-- [ ] Write tests: verify E2E test #1 baseline values (spec §21)
-- [ ] **Commit checkpoint**
+- [x] Create migration for egg_stats_30d_by_location table
+- [x] Implement bird-days calculation from intervals
+- [x] Implement layer-eligible days filtering
+- [x] Implement feed proration formula
+- [x] Implement cost calculations (integer cents)
+- [x] Create `services/stats.py` with get_egg_stats (compute on read)
+- [x] Write tests: verify E2E test #1 baseline values (spec §21)
+- [x] **Commit checkpoint** (c08fa47)
 
 ### Step 4.5: Product Sold Event
 - [ ] Implement apply_product_sold projection