feat(admin-console): Stage 2 — dashboard monitoring

Turn the console landing page into an operational dashboard.

- new internal/opsstatus: read-only Postgres projection via go-jet — ping +
  per-status COUNT/GROUP BY on runtime_records, mail_deliveries,
  notification_routes, and a malformed-intent count; degrades per-probe into
  Snapshot.Errors rather than failing the page
- dashboard renders backend readiness, database health, the three status
  tables, the malformed count, and any collection errors; falls back to a
  "monitoring not wired" note when no reader is injected
- AdminConsoleHandlers now takes an AdminConsoleDeps struct (Monitor + Ready
  added) so later stages add service refs without churning the signature

Tests: opsstatus store test against a Postgres testcontainer (empty schema +
one enqueued delivery); dashboard render tests with a fake reader (with and
without monitoring).

Docs: ARCHITECTURE 14.1 + FUNCTIONAL 10.2.1 (+ru) describe the dashboard.
(Prometheus /metrics exporters were already enabled in dev-deploy in Stage 1.)

backend/internal/adminconsole/dashboard.go

@@ -0,0 +1,24 @@
+package adminconsole
+
+// StatusCount pairs a status label with its current row count for the
+// dashboard's per-status tables. It is the view-layer counterpart of the
+// data gathered by the ops-status reader; the server handler maps between
+// them so this package stays free of database concerns.
+type StatusCount struct {
+	Status string
+	Count  int64
+}
+
+// DashboardData is the view model for the console landing page. MonitorAvailable
+// is false when no ops-status reader is wired, in which case the monitoring
+// panels are omitted. Errors carries non-fatal probe failures for display.
+type DashboardData struct {
+	MonitorAvailable      bool
+	BackendReady          bool
+	PostgresHealthy       bool
+	Runtimes              []StatusCount
+	MailDeliveries        []StatusCount
+	NotificationRoutes    []StatusCount
+	NotificationMalformed int64
+	Errors                []string
+}