fix: persist service host port; demo-data scope for telemetry

Public URLs were ephemeral: every restart/redeploy rebound a random host
port, so endpoint links rotted. Persist published_port on the service and
prefer it for replica 0 on create. If the port is taken, fall back to
ephemeral and repersist the new assignment. Post-start the binding is
verified — Docker Desktop accepts a conflicting publish silently, which
previously left services running with no endpoint at all.

demo-data.ts gains the required scope field for HostMonitoring (CI fix).

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app/backend/migrations_goose/20261003120000_service_published_port.sql

@@ -0,0 +1,8 @@
+-- +goose Up
+-- Stable public host port for service replica 0. 0 means "not yet assigned";
+-- the runtime writes the ephemeral port it picked back here so restarts and
+-- redeploys keep the same public endpoint instead of churning.
+ALTER TABLE public.services ADD COLUMN IF NOT EXISTS published_port integer NOT NULL DEFAULT 0;
+
+-- +goose Down
+ALTER TABLE public.services DROP COLUMN IF EXISTS published_port;