stacks: use each app's real default port instead of arbitrary fleet ports

Replaced 29 host-port values across 27 stacks with the app's own
well-known default (read directly from each compose file's own
container-side port mapping) instead of the arbitrary port numbers
this fleet actually assigns to avoid collisions across ~44 services
on one host. More recognizable to a reader, and removes the last
fleet-specific detail these files carried.

Also removes a stale adminer service from n8n's stack entirely
(compose service + .env var) - it's no longer actually deployed.

stacks/productivity/n8n/.env

@@ -1,7 +1,6 @@
 # Exposed HTTP port
 N8N_PORT=5678
-POSTGRES_PORT=5442
-ADMINER_PORT=8091
+POSTGRES_PORT=5432
 N8N_HOST=n8n.local.example.com
 
 # System time zone

stacks/productivity/n8n/docker-compose.yaml

@@ -50,15 +50,6 @@ services:
     networks:
       - n8n-net
 
-  adminer:
-    image: adminer:latest
-    container_name: adminer
-    restart: unless-stopped
-    ports:
-      - "127.0.0.1:${ADMINER_PORT}:8080"
-    networks:
-      - n8n-net
-
 networks:
   n8n-net:
     external: true