Docs: bring all documentation current with v0.8.1

- README: v0.8.1 highlights, Node 18+ requirement + client install step for
  manual dev setup, health/genetics features listed, release summary updated
- API.md: paginated response shapes for dogs/litters, validation + status-code
  behavior (400/404), full breeding heat-cycle CRUD, genetics PUT/DELETE,
  pedigree COI/relations/cancer-lineage endpoints, corrected Litter object
- DEVELOPMENT.md: two-layer migration approach documented with schema-drift
  warning, heat_cycles/cancer_history tables, Toast/ConfirmDialog UI patterns
  (no alert/window.confirm), full env-var table, auth-deferred decision noted
- INSTALL.md: fixed API smoke-test (old /api/health root path doesn't exist),
  master -> main
- ROADMAP: v0.8.1 entry; Phase 4b checkboxes reconciled with what's actually
  built; Phase 6 progress; pre-deploy prod-DB check added to QA list

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

INSTALL.md

@@ -113,14 +113,14 @@ Access: http://localhost:3000
 ================================
 ```
 
-### Test Health Endpoint
+### Test the API
 ```bash
-curl http://localhost:3000/api/health
+curl http://localhost:3000/api/settings
 ```
 
-Should return:
+Should return the kennel settings JSON, e.g.:
 ```json
-{"status":"ok","timestamp":"..."}
+{"id":1,"kennel_name":"BREEDR", ...}
 ```
 
 ---
@@ -136,7 +136,7 @@ docker rm breedr
 
 # Pull latest code
 cd /tmp/breedr
-git pull origin master
+git pull origin main
 
 # Rebuild image
 docker build -t breedr:latest .