[Discussion 2/3] Retire native Usage workspace

[sarthakagrawal927]

Native slice

Retire the general Usage workspace from the macOS viewer. Navigation and the command palette omit it; the legacy --ui-test-section Usage route opens Explore. Remove the now-unused native usage views, models, snapshots, rendering tests, and provider icon assets. Verification-run cost evidence and History recovery controls remain.

This is PR 2 of 3 for #328, based on #330. The CLI commands and capability registry remain in this intermediate slice; PR #329 removes those and updates the documentation. Review the stack together before merging or releasing.

Checks

• Change-size gate: 28 files, 4,664 gross lines, pass.
• Focused native navigation test, capability registry parity, full background native suite, staged whitespace check, and pre-push lint/Gitleaks: pass.
• Offscreen owner-review packet: 99 Swift tests passed; 35 current renders finalized, with no retired Usage card or missing image.
• No foreground automation, installed-app check, or release was performed.