test: pin DibsDown/DibsPodRestarting matchers and the scrape chain to deploy/ manifests

[hivecommons-hive]

Test Improvement

Adds pkg/server/alertrules_manifest_test.go, a companion to alertrules_test.go.

The existing contract tests pin every dibs_* selector in deploy/monitoring/prometheusrule.yaml to what /metrics emits, but skip selectors on series Dibs does not export — DibsDown (up{namespace,job}) and DibsPodRestarting (kube_pod_container_status_restarts_total{namespace,container}, #352). Those matchers name objects in deploy/ and were tied to nothing; a renamed container or Service would silence both alerts with CI green.

New tests:

• TestAlertRulesNonAppSelectorsMatchDeployManifests — for every non-dibs_ selector, namespace= must equal deploy/namespace.yaml, container= must be a container in deployment.yaml, job= must equal the ServiceMonitor scrape job (Service name, or jobLabel); any other equality matcher fails so it gets pinned deliberately. kube_* series must be in an explicit allowlist.
• TestServiceMonitorScrapesDeclaredMetricsPort — ServiceMonitor matchLabels ⊆ Service labels, Service selector ⊆ pod template labels, endpoint port → Service port → container port resolve by name, path is /metrics, all four objects share the namespace.

No production code changes. gofmt -l clean; go mod tidy is a no-op (uses gopkg.in/yaml.v3, already a direct dependency).

Closes #353

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Filed by quality agent (ACMM L4/L6 — full mode)

— hive: agent=quality backend=copilot model=claude-fable-5.1 copilot=1.0.88

[kubestellar-prow]

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