feat(enterprise): stream trace uploads to scoped storage

[Gracker]

Summary

• Stream /api/traces/upload-url response bodies directly to uuid .uploading files via pipeline instead of arrayBuffer().
• Store multipart temp files in the scoped trace directory with uuid names, then rename to {traceId}.trace to avoid original-filename collisions.
• Add upload limit resolution from SMARTPERFETTO_TRACE_UPLOAD_MAX_BYTES / RAM-derived budget with a 1 GiB cap, and mark README §0.4.2 complete.

Verification

• cd backend && npx jest --runInBand --forceExit src/routes/tests/enterpriseTraceMetadataRoutes.test.ts
• cd backend && npm run typecheck
• cd backend && npx jest --runInBand --forceExit src/routes/tests/enterpriseTraceMetadataRoutes.test.ts src/routes/tests/ownerGuardRoutes.test.ts src/routes/tests/workspaceResourceRoutes.test.ts
• git diff --check
• cd backend && npm run test:scene-trace-regression
• cd backend && npx jest --runInBand --forceExit src/agentv3/tests/analysisPatternMemory.test.ts
• cd backend && npm run test:core
• npm run verify:pr

Note: the first test:core run hit an existing order-sensitive analysisPatternMemory assertion; rerunning that suite and test:core passed before verify:pr, and verify:pr passed end-to-end.

Stacked on #82 / feature/enterprise-multi-tenant-restart-persistence-tests.