feat: create net stack consolidating proxy, netdata, watchtower, and umami

- Create net/compose.yaml with 4 services (traefik, netdata, watchtower, umami)
- Update arty.yml with NET_* environment variables
- Update compose.yaml to include net instead of individual stacks
- Update restic volume references to net_letsencrypt_data and net_netdata_config
- Copy configuration files to net/ directory (Dockerfile, dynamic/, go.d/, etc.)

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

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

net/go.d/filecheck.conf

@@ -0,0 +1,5 @@
+jobs:
+  - name: restic_repository
+    dirs:
+      include:
+        - '/mnt/hidrive/users/valknar/Backup'

net/go.d/postgres.conf

@@ -0,0 +1,3 @@
+jobs:
+  - name: docker_core_postgres
+    dsn: 'postgres://netdata:netdata_monitor_password@172.18.0.5:5432/postgres'