perf(web): parallelize scoped GRC overview reads

[jonathanhaaswriter]

Summary

• start the GRC dashboard and readiness reads together instead of waiting for dashboard data
• apply the active tenant and workspace selectors to both request paths
• reject workspace-only scope before issuing GRC reads and disable Refresh for that invalid state
• cover parallel loading, scope isolation, and both Refresh paths in the GRC page test

Validation

• focused ESLint for the changed page and test
• 18 focused Home, GRC, and scope tests
• fixture E2E: 13 route contracts with Chromium checks
• optimized Next.js build and standalone smoke
• browser waterfall: both scoped GRC reads start in the same millisecond and complete successfully
• route entry bundle: 7 chunks, 257,404 raw bytes (+517 bytes versus the measured base)

The repository-wide test run reaches 700 passing tests and one existing Node 26 localStorage setup failure in the GRC client mutation test; the changed-path suite passes.