chore: simplify footer and add Noisens maintainer attribution

[DeepZone]

Motivation

• The global footer contained runtime technical details (mode, read-only, etc.) that are noisy for persistent navigation and better suited to system/dashboard views.
• A small maintainer attribution is needed in an informational, non-prominent place to credit ongoing maintenance.

Description

• Simplified the footer/system line in frontend/src/App.tsx by replacing the previous systemLine with a minimal display: when available ${system.name} · ${system.version} and fallback RouteForge · v1.0.0.
• Removed runtime technical details from the global footer such as mode=..., read_only=..., and similar status markers so they no longer appear in the global footer.
• Added a subtle maintainer note to the About section in frontend/src/App.tsx as <p className='text-xs text-slate-500'>Maintained by Norman Sens.</p>.
• No changes to feature logic, read-only security model, database migrations, language, or versioning were made.

Testing

• Ran the frontend production build with cd frontend && npm run build, which completed successfully.

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Codex Task