feat(enterprise): add lease admin controls

[Gracker]

Summary

• Add runtime:manage RBAC permission for workspace/org admins.
• Add admin-only POST /api/tp/:leaseId/drain to move a scoped trace processor lease into draining and block new proxy work.
• Add admin-only POST /api/tp/:leaseId/restart to restart a scoped lease through the single lease supervisor while preserving the lease id.

Scope notes

• Advances README §11.11 row: 24h timeout must not be the only answer for hung queries; operators can explicitly drain or restart the lease.
• Does not close README §0.4.12 because the full §11.11 checklist still has other rows and final design-audit evidence outstanding.
• README TODO state is unchanged.

Validation

• cd backend && PATH="$HOME/.nvm/versions/node/v24.15.0/bin:$PATH" npx jest --runInBand --forceExit src/services/__tests__/rbac.test.ts src/routes/__tests__/traceProcessorProxyRoutes.test.ts src/services/__tests__/traceProcessorLeaseProcessorRouting.test.ts
• cd backend && PATH="$HOME/.nvm/versions/node/v24.15.0/bin:$PATH" npm run typecheck
• cd backend && PATH="$HOME/.nvm/versions/node/v24.15.0/bin:$PATH" npm run test:core
• PATH="$HOME/.nvm/versions/node/v24.15.0/bin:$PATH" npm run verify:pr

[Gracker]

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