feat: real service runtime — private networks, replicas, lifecycle, rollback

Services now reconcile into actual Docker containers instead of
bookkeeping rows:

- Per-project bridge network with service-name DNS aliases and
  ${{service.KEY}} env expansion (HOST/PORT builtins)
- Replicas, published ports, Traefik domain routing, health checks,
  restart policies persisted on the service spec; spec-hash drift
  recreates containers on redeploy
- Lifecycle API: start/stop/restart/redeploy, live runtime state,
  real image rollback (replaces the fake sleep)
- Manual scale and PUT replicas reconcile live containers; service
  and project delete remove their containers and the project network
- Canvas: real URLs, replica badges, env filter, right-click
  deploy/restart/stop/delete menu, empty state
- Service detail: real lifecycle buttons, live replica/URL strip,
  Networking editor, ${{ }} variable helper
- Fix prebuilt-image pulls racing the tag (drain the pull stream)

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

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

app/backend/migrations_goose/20260923000000_service_runtime.sql

@@ -0,0 +1,16 @@
+-- +goose Up
+-- Runtime spec for Railway-style services: replica count, the container port
+-- to expose, an optional public domain routed via Traefik, healthcheck path
+-- and restart policy.
+ALTER TABLE public.services ADD COLUMN IF NOT EXISTS replicas integer NOT NULL DEFAULT 1;
+ALTER TABLE public.services ADD COLUMN IF NOT EXISTS port integer NOT NULL DEFAULT 0;
+ALTER TABLE public.services ADD COLUMN IF NOT EXISTS domain character varying(500) NOT NULL DEFAULT '';
+ALTER TABLE public.services ADD COLUMN IF NOT EXISTS healthcheck_path character varying(500) NOT NULL DEFAULT '';
+ALTER TABLE public.services ADD COLUMN IF NOT EXISTS restart_policy character varying(50) NOT NULL DEFAULT 'unless-stopped';
+
+-- +goose Down
+ALTER TABLE public.services DROP COLUMN IF EXISTS replicas;
+ALTER TABLE public.services DROP COLUMN IF EXISTS port;
+ALTER TABLE public.services DROP COLUMN IF EXISTS domain;
+ALTER TABLE public.services DROP COLUMN IF EXISTS healthcheck_path;
+ALTER TABLE public.services DROP COLUMN IF EXISTS restart_policy;