#7219 improvement(usage): add a period-labelled chart to the workspace drill-down

Summary

• The Workspaces drill-down in the enterprise usage panel showed two ranked lists and no chart, and stated its window nowhere — the period picker lives on the list behind it, so the carried-over window was invisible once you were inside.
• Draw the summary's headline, delta, and trend chart at the top of the drill-down, narrowed to that workspace.
• Label that section with the selected period (Current period, Last 30 days, Aug 1 - Aug 28), which is now the only place the drill-down states its window.
• Carry workspaceId through the summary contract, route, use case, query key, and hook so the chart reads one workspace.
• Move the workspace narrowing onto buildUsageAnalyticsScope, so the chart, the headline, and both lists derive it from one definition instead of the breakdown query owning a second copy.

Two details worth a look in review:

• The comparison window takes the same narrowing, or the delta would measure one workspace against the whole organization.
• No allowance figure, unlike the Overview: the limit is pooled across the organization and under one workspace's total would read as that workspace's own cap.

workspace_id is not in usage_log_billing_entity_created_at_cost_idx, so a narrowed read heap-fetches per row — the cost the Workspaces list already pays to rank itself, and only paid inside a drill-down.

Type of Change

• Improvement (UI + supporting API scope)

Testing

• bun run test — 1,649 tests pass across ee/, lib/api/contracts, and the usage analytics/application suites; full lib/billing suite (731) passes
• Added coverage: the scope narrowing survives all three window branches, and the summary's comparison window takes the same workspace filter
• bun run type-check, bun run lint, bun run check:audits (38 audits incl. check:api-validation:strict, check:react-query, check:client-boundary) all pass
• Not verified against a running instance — it needs a live enterprise organization with populated usage logs

Checklist

• Code follows project style guidelines
• Self-reviewed my changes
• Tests added/updated and passing
• No new warnings introduced
• I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)