fix(Chunk4): purge all Pi-hole references from split files

- 08-deployment-phases: Pi-hole → AdGuard Home in Phase 1 order
- 09-open-questions: blocker replaced, decision marked resolved
- 10-appendix: removed from DockerHub table, count 16→15, dir pihole/→adguard/
- 05-network-architecture: port allocation DNS label updated
- All mirrored to master PRD

homelab-services-stack-prd.md

@@ -432,7 +432,7 @@ traefik.http.middlewares.authelia.forwardauth.address: http://authelia:9091/api/
 ~/.ansible-repo/new-build/
 ├── phase-1/                    # Infrastructure
 │   ├── technitium/
-│   ├── pihole/
+│   ├── adguard/
 │   ├── traefik/
 │   ├── authelia/
 │   ├── portainer/