feat: add runtime policy to desktop desk

[xiaojiou176]

Summary

• add control_plane_runtime_policy to the desktop Policies page so desktop operators can inspect the same runtime-governance surface that web already exposes
• update the desktop policies test fixture to cover the new section and confirm the rendered payload
• keep the change read-only: no new mutation surface, no authority change

Why

• web already surfaces control_plane_runtime_policy, but desktop Policies was still missing that section
• this patch closes a narrow desktop/web parity gap for completion-governance visibility
• it gives desktop operators a direct read surface for dod_checker / reply_auditor / continuation_policy policy data without inventing a new API contract

Verification

• pnpm --dir apps/desktop exec vitest run src/pages/overview_policies_branch.test.tsx src/pages/desktop_p1_controls.test.tsx
• pnpm --dir apps/desktop exec tsc -p tsconfig.json --noEmit
• npm run truth:triage (repo-side green; external truth still red only on the known Docker/platform upstream records: ci-core-image.json and ui-audit-playwright.json)

Scope guard

• This wave does not change write behavior or desktop action authority.
• It only adds read-only parity for the existing runtime policy surface.