feat(metrics): add pod CPU/memory usage history with charts drawer

[wellCh4n]

metrics-server keeps no history, so the status page could only show a point-in-time reading. This adds an in-process sampler that turns those readings into 24 hours of per-pod usage curves.

Backend:

• PodMetricSampleJob sweeps every environment on a 30s tick, fanning out across virtual threads so one unreachable cluster cannot delay the others. Each environment costs two cluster-wide API calls (pod list + top) regardless of application count; pods are attributed to applications via the oops.app.name label, so the sweep never touches the database.
• InMemoryPodMetricHistoryStore keeps each pod series in a fixed-size ring of primitive arrays (20 bytes/sample, ~57KB per pod for 24h) behind the PodMetricHistoryStore port. Series survive pod deletion until their samples age out, so charts drawn right after a rollout still show the replaced pods. A max-series cap guards the heap.
• GET .../applications/{name}/metrics/history?env=&range=&agg= serves chart-ready series. Buckets are epoch-aligned and floored at two sampling intervals so the avg/max choice is meaningful on every range; long ranges downsample to at most 240 points per pod.
• spring.task.scheduling.pool.size is raised to 3 in the config templates: the Spring Boot default of 1 would serialise this sampler with PipelineInstanceScanJob and ScheduledRestartJob.

Frontend:

• A "Metrics" button on the status page's environment tab row opens a right-side drawer with two area charts (CPU cores, memory MiB), one line per pod, with 30m/1h/6h/24h ranges, an avg/max toggle, and a 30s silent refresh. Localised in all four languages.
• Adds the base-vega chart (recharts) and drawer components; tabs get cursor-pointer per project convention and a primary-colored active indicator for the line variant.

History lives in memory by design (restart starts over) and shares the single-instance assumption of the existing scheduler jobs; the store port isolates a future shared-storage implementation if that changes.