feat(v5): gate V5 to development environments only

Introduce V5Feature and config so V5 routes, jobs, commands, morph maps,
and model queries run only when enabled. Move V5 migrations to
migrations-v5 (loaded only when enabled), remove Flux from production
Docker/install paths, and add isolation tests.

scripts/install.sh

@@ -228,12 +228,11 @@ if [ "$WARNING_SPACE" = true ]; then
     sleep 5
 fi
 
-mkdir -p /data/coolify/{source,ssh,applications,databases,backups,services,proxy,sentinel,flux}
+mkdir -p /data/coolify/{source,ssh,applications,databases,backups,services,proxy,sentinel}
 mkdir -p /data/coolify/ssh/{keys,mux}
 mkdir -p /data/coolify/proxy/dynamic
 
 chown -R 9999:root /data/coolify
-chown -R 9999:root /data/coolify/flux
 chmod -R 700 /data/coolify
 
 INSTALLATION_LOG_WITH_DATE="/data/coolify/source/installation-${DATE}.log"

scripts/upgrade.sh

@@ -171,9 +171,6 @@ else
     log "Network 'coolify' already exists"
 fi
 
-mkdir -p /data/coolify/flux
-chown -R 9999:root /data/coolify/flux
-
 # Fix SSH directory ownership if not owned by container user UID 9999 (fixes #6621)
 # Only changes owner — preserves existing group to respect custom setups
 SSH_OWNER=$(stat -c '%u' /data/coolify/ssh 2>/dev/null || echo "unknown")