feat: compact Agent overview cards

[yujiezhang-ops]

Closes #33

Summary

• Keep rights-safe generic Agent marks while restoring visual hierarchy through controlled UI accent colors.
• Replace repeated Provider/Profile/Model/Version headings with compact status and metadata pills.
• Hide URL, npm package, detection notes, and raw configuration diagnostics behind a native Details disclosure.
• Reduce per-row actions to text-first controls: conditional configuration, update, launch, and one details disclosure; remove decorative action icons except the loading spinner.
• Give Launch the primary action treatment and keep the list/cards within a readable max width.
• Suppress empty Not recorded fields and show concise Not configured/Not linked states.
• Update the overview description and tests to match the new information hierarchy.

Tests

• cd frontend && pnpm run test — 22 files, 144 tests passed
• cd frontend && pnpm run build — typecheck and Vite production build passed

This change does not restore unaudited third-party brand artwork and is related to the rights-safe direction in #25.