v0.9.1-rc: UI Cleanup & English-Only Product Polish

[DeepZone]

Motivation

• The UI contained mixed German/English copy, verbose developer/demo text and some noisy helper copy that reduces product clarity.
• The goal is a compact, product-facing, English-only operator experience while preserving read-only and security/migration warnings.
• No business logic, API contracts or migrations are changed; this is purely UI/text/layout polishing for v0.9.1-rc.

Description

• Replaced German and verbose strings with concise English across the main UI, including dashboard, header, About page, reports and report detail views, and key forms; updated App.tsx, Layout.tsx, ReportView.tsx and multiple form components (ASN/Prefix/Preflight/BGP/ROA) to English copy and compact phrasing.
• Simplified the Dashboard to show product name/version, current user, role, read-only status, mode and compact Quick Actions, and kept migration/security warnings concise and prominent (frontend/src/App.tsx).
• Standardized empty states and labels (e.g. No reports yet., No change cases yet., No audit entries found., No users found., No runs yet.) and unified button labels and export actions (Copy Summary, Download Markdown, Download HTML).
• Removed a browser confirm() prompt from Change Case deletion (now deletes without a browser confirm) and adjusted tidy copy in Change Cases, Watch Mode, Users, Audit Log and Report export hints; added a short release note entry for the UI polish (RELEASE_NOTES.md).

Testing

• Ran frontend production build with cd frontend && npm run build, which completed successfully. ✅
• Backend tests (cd backend && pytest -q) were not run because this PR only updates frontend UI strings and release notes and does not modify backend source or behavior; no backend code/migrations were changed.
• Manual review of the updated screens was performed by verifying the built assets and inspecting the modified components listed above.

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Codex Task