fix(cli): clarify agent console preview formatting

[codeaholicguy]

Summary

• format preview turns consistently with ai-devkit agent detail
• show timestamped, colored role headers with neutral indented message bodies
• preserve blank lines and Markdown structure while clearly separating turns
• identify the speaker when scrolling begins inside a continued message
• enable Ink incremental rendering at 60 FPS for responsive preview scrolling
• add viewport, render-policy, and ANSI-safe Ink regression coverage

Performance

• viewport construction: about 0.041 ms per call for 20 messages with 80 lines each
• synthetic 40-row rapid-update benchmark: terminal output reduced from 49,793 bytes to 5,793 bytes (88% reduction)
• wide PTY smoke test confirmed changed-line updates without layout corruption

Validation

• npm test --workspace ai-devkit -- --run src/__tests__/tui/console (125 tests passed)
• npm run build --workspace ai-devkit
• full pre-commit nx run-many -t lint and nx run-many -t test (957 tests passed)

Risks

• Message headers and separators consume additional preview rows, trading density for scanability and consistency with agent detail.
• Incremental rendering relies on Ink 7 terminal cursor updates; verified in the alternate-screen PTY smoke test.
• Existing unrelated lint warnings remain unchanged.