v0.9.2-rc: English-Only Output & Text Cleanup

[DeepZone]

Motivation

• The project still emitted German user-facing text in backend checks, API error details, and generated reports despite prior UI cleanup, so all runtime-visible strings must be English-only for consistency and clarity.
• The release should reflect the new patch candidate version v0.9.2-rc across visible surfaces.

Description

• Translated user-facing strings from German to English across backend services including RPKI, ASN, prefix, BGP visibility, routing visibility, ROA planner, registry checks, recommendations, and prefix evaluation, preserving logic and status values.
• Converted report templates (backend/app/templates/report.md.j2 and report.html.j2) headers and labels to English so generated Markdown/HTML outputs are English-only and kept diagnostics content intact.
• Replaced German API error/detail messages in check routes (backend/app/api/routes_checks.py) and standardized frontend fallback error message in frontend/src/api.ts to English without changing HTTP codes or flows.
• Bumped backend/frontend package and visible app versions to 0.9.2 / v0.9.2-rc in backend/pyproject.toml, backend/app/main.py, backend/app/core/system_status.py, backend/app/api/routes_system.py, frontend/package.json, frontend/src/App.tsx, and updated related docs (README.md, ROADMAP.md, RELEASE_NOTES.md).
• Updated tests that depended on the old version string (backend/tests/test_api_smoke.py) and preserved existing test semantics.

Testing

• Ran backend tests with cd backend && pytest -q, final result: 102 passed, 0 failed, with warnings reported (tests passed after fixing version expectation).
• Built the frontend with cd frontend && npm run build, build completed successfully (vite build output produced dist/ files).
• Verified that the system status and report generation flows return English text and that API error responses remain functionally unchanged (only detail strings translated).

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Codex Task