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>

roles/docker/templates/postiz-compose.yml.j2

@@ -5,9 +5,9 @@ services:
     restart: always
     environment:
       # You must change these. Replace `postiz.your-server.com` with your DNS name - what your web browser sees.
-      MAIN_URL: "https://post.thesatelliteoflove.com"
-      FRONTEND_URL: "https://post.thesatelliteoflove.com"
-      NEXT_PUBLIC_BACKEND_URL: "https://post.thesatelliteoflove.com/api"
+      MAIN_URL: "https://{{ subdomains.post }}"
+      FRONTEND_URL: "https://{{ subdomains.post }}"
+      NEXT_PUBLIC_BACKEND_URL: "https://{{ subdomains.post }}/api"
       JWT_SECRET: "TShr6Fdcwf67wIhuUvg0gOsJbdcQmgMiJl5kUh6JCfY="
  
       # These defaults are probably fine, but if you change your user/password, update it in the
@@ -24,7 +24,7 @@ services:
 
       # Social keys
       LINKEDIN_CLIENT_ID: "86q7ksc8q5pai3"
-      LINKEDIN_CLIENT_SECRET: {{ linkedin_secret }}
+      LINKEDIN_CLIENT_SECRET: {{ vault_postiz.linkedin_secret }}
     volumes:
       - postiz-config:/config/
       - postiz-uploads:/uploads/
@@ -35,7 +35,7 @@ services:
         condition: service_healthy
     labels:
       glance.name: Postiz
-      glance.url: https://post.thesatelliteoflove.com/
+      glance.url: https://{{ subdomains.post }}/
       glance.description: Social media scheduler
       glance.id: postiz
  
@@ -90,4 +90,4 @@ volumes:
 networks:
   default:
     external: true
-    name: lava
+    name: {{ docker.network_name }}