feat(keywords): add native market insights UI

[hubab1]

Summary

• add an accessible Market Insights toolbar action and native macOS sheet
• freeze the selected app/platform/country scope while clearly excluding workspace search, date, and metric filters
• present coverage, best/worst/average/spread, all seven per-market states, cached failures, stale evidence, bounded-read uncertainty, and difficulty provenance
• support generation-safe loading, explicit reload, terminal refresh completion updates, bounded pagination, restart recovery, and live detail selection by row identity
• distinguish empty scope, empty result, initial failure, retained-data failure, pagination failure, partial evidence, and stale evidence without making network requests

Dependency and review gate

This draft is stacked on the item 23 foundation PR. It is Category C and must not merge before maintainer UX approval.

Manual review should cover loading, retained-data refresh, initial and pagination failures, empty scope, every partial/stale state, large country scopes, nested details, minimum-size layout, keyboard navigation, and VoiceOver.

No live app launch was performed because this stack inherits schema V4.

Validation

• item 23 and shared service focused suites: 38/38 passed
• exact final tree: 446/446 full tests passed
• signed Debug build passed; strict codesign verification passed
• project plist lint and diff check passed
• two independent final reviews found no remaining P0, P1, P2, or actionable P3 findings
• combined tree SHA: 36036267702f7b4b3701dc949aadf46d866dfc61

Reference

Independent native implementation informed by the market-insights direction in WIP PR #8 commit akshaynexus@441b871. Source reference only.