feat: complete variable management implementation and update documentation

- Update remaining Docker Compose templates with centralized variables
- Fix service tag isolation to deploy individual services only
- Update all README files with variable management architecture
- Document variable hierarchy in DEPLOYMENT_LEARNINGS.md
- Add comprehensive variable usage patterns to CLAUDE.md
- Standardize domain references using {{ subdomains.* }} pattern
- Replace hardcoded network names with {{ docker.network_name }}
- Update hairpinning configuration to use variables

🤖 Generated with [Claude Code](https://claude.ai/code)

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

group_vars/all/domains.yml

@@ -17,11 +17,11 @@ subdomains:
   models: "models.{{ primary_domain }}"  # Manyfold
   pinchflat: "pinchflat.{{ primary_domain }}"
   pin: "pin.{{ primary_domain }}"  # Pinry
-  papers: "papers.{{ primary_domain }}"  # Paperless-NGX
+  paper: "paper.{{ primary_domain }}"  # Paperless-NGX
   tasks: "tasks.{{ primary_domain }}"  # MMDL
   syncthing: "syncthing.{{ primary_domain }}"
   loclog: "loclog.{{ primary_domain }}"  # Dawarich
-  pingvin: "pingvin.{{ primary_domain }}"
+  files: "files.{{ primary_domain }}"  # Pingvin file sharing
   social: "social.{{ primary_domain }}"  # GoToSocial
   post: "post.{{ primary_domain }}"  # Postiz
   home: "home.{{ primary_domain }}"  # Glance