feat(enterprise): add trace processor lease holders

[Gracker]

Summary

• Add TraceProcessorLeaseStore with scoped TraceProcessorLease and holder records for frontend_http_rpc, agent_run, report_generation, and manual_register.
• Implement the §11.4 lease state machine plus graded holder TTL policies for visible/hidden/offline frontend holders, manual registration, agent runs, and report generation.
• Wire enterprise-mode lease acquisition into trace upload/get/register/stats routes and agent analyze/report generation paths.
• Extend enterprise schema migration to persist holder expiry and metadata, and mark §0.4.4 complete in the enterprise TODO.

Validation

• cd backend && npx jest --runInBand --forceExit src/routes/__tests__/agentRoutesRbac.test.ts src/services/__tests__/traceProcessorLeaseStore.test.ts
• cd backend && npx jest --runInBand --forceExit src/services/__tests__/traceProcessorLeaseStore.test.ts src/routes/__tests__/enterpriseTraceMetadataRoutes.test.ts src/scripts/__tests__/verifyEnterpriseMultiTenantWindows.test.ts
• cd backend && npm run typecheck
• git diff --check
• cd backend && npm run test:core
• cd backend && npm run test:scene-trace-regression
• npm run verify:pr

[Gracker]

已通过 commit 67856ec (merge) + 023a84a (frontend rebuild) 合入 main，关闭此 PR。