feat(nodes): remote ingress via Traefik file provider

Remote replicas publish an ephemeral host port; the agent reports the
assigned binding back in the create_container result and the backend
renders a per-service file-provider config into TRAEFIK_DYNAMIC_DIR
pointing Traefik at the node's mesh IP + port. Routes are rewritten on
every remote reconcile and removed on teardown or local placement.

Also: RetireService retires remote leftovers when a service returns to
local placement; remove_container is idempotent agent-side; tombstoned
replicas skip remove dispatch; the domains-stay-local ceiling is gone.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

.env.example

@@ -49,6 +49,10 @@ CONTAINR_AGENT_AUTH_TOKEN=replace_with_strong_agent_secret
 # CONTAINR_AGENT_AUTH_TOKENS=current_secret,next_secret
 # Bundled agent binaries dir served at /api/agents/download/:platform.
 # CONTAINR_AGENT_BIN_DIR=/agents
+# Directory Traefik's file provider watches. The backend writes one
+# config per remote service here so domains route to node agents. The
+# infra compose wires a shared volume — set only for custom layouts.
+# TRAEFIK_DYNAMIC_DIR=/traefik-dynamic
 # Optional remote template catalog (another Containr instance). Its
 # templates merge into GET /templates as source:"registry" and
 # materialize locally on deploy. The bundled catalog works without it.