feat(enterprise): block direct RPC registration

[Gracker]

Summary

• disable the legacy /api/traces/register-rpc naked-port compatibility endpoint when enterprise mode is enabled
• add an enterprise route regression test proving no external RPC registration, trace metadata, or lease rows are created

Validation

• cd backend && PATH="$HOME/.nvm/versions/node/v24.15.0/bin:$PATH" npx jest --runInBand --forceExit src/routes/__tests__/enterpriseTraceMetadataRoutes.test.ts src/routes/__tests__/ownerGuardRoutes.test.ts src/services/__tests__/traceProcessorService.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

TODO

• Advances README §0.4.12 / §11.11: ExternalRpc/register-rpc compatibility path no longer creates enterprise-mode naked-port state.
• README §0.4.12 remains unchecked until every §11.11 row is verified.
• README §0.4.3 remains blocked on the required large trace RSS matrix.

[Gracker]

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