feat: use ${SUBDOMAIN} variable in all templates

All 51 docker-compose.yml: replaced hardcoded subdomain.${DOMAIN}
with ${SUBDOMAIN}.${DOMAIN} in Traefik labels, app env vars, and
comments.

All 51 .felhom.yml: added SUBDOMAIN deploy field (type: subdomain)
with default matching existing subdomain metadata value.

Works with felhom-controller v0.27.0 which validates and stores the
user-chosen subdomain in app.yaml. Existing deployed apps get
SUBDOMAIN auto-injected via InjectMissingFields() on next sync.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

templates/actualbudget/.felhom.yml

@@ -29,6 +29,14 @@ deploy_fields:
     description: "A szerver domain neve"
     locked_after_deploy: true
 
+  - env_var: SUBDOMAIN
+    label: "Aldomain"
+    type: subdomain
+    default: "budget"
+    required: true
+    locked_after_deploy: true
+    description: "Az alkalmazás aldomainje"
+
 # --- App info (info page content) ---
 app_info:
   tagline: 'Költségvetés tervező - pénzügyeid kézben tartása egyszerűen'

templates/actualbudget/docker-compose.yml

@@ -1,5 +1,5 @@
 # ActualBudget - Personal Finance / Budgeting
-# Domain: budget.${DOMAIN}
+# Domain: ${SUBDOMAIN}.${DOMAIN}
 # Database: None (file-based)
 # RAM: ~50MB (mem_limit: 256M) | Pi-compatible: Yes
 #
@@ -32,7 +32,7 @@ services:
       start_period: 10s
     labels:
       - "traefik.enable=true"
-      - "traefik.http.routers.actualbudget.rule=Host(`budget.${DOMAIN}`)"
+      - "traefik.http.routers.actualbudget.rule=Host(`${SUBDOMAIN}.${DOMAIN}`)"
       - "traefik.http.routers.actualbudget.entrypoints=websecure"
       - "traefik.http.routers.actualbudget.tls=true"
       - "traefik.http.routers.actualbudget.tls.certresolver=letsencrypt"