feat: streamline human review detail previews

[steve8708]

Summary

• Reduce Human Review detail-view density by moving written feedback and instruction drafts into focused popovers.
• Add an opt-in output preview for text, charts, tables, images, and design payloads.
• Keep the preview bounded and safe, with localized controls and parser coverage.

Validation

• pnpm --filter @agent-native/core exec vitest run src/client/observability/OutputPreview.spec.ts
• pnpm --filter @agent-native/core exec tsc --noEmit --pretty false
• pnpm guards
• Verified the compact table, sparse detail, preview, feedback popover, and instruction popover in the running Factory app.