Antigravity Usage — status-bar segment disappears while toggle is checked (W28)

In Orca 1.4.128, the status-bar Antigravity Usage toggle can be checked while the actual Antigravity usage segment disappears from the status bar.

**Status:** active
**Next:** Port the local hotpatch into the source build and add a regression test for the status-bar visibility contract.
**Source artifact:** user screenshot/report from 2026-07-08; local verification reproduced against packaged renderer chunks.
**Date:** 2026-07-08

## Scope
- [ ] Treat `antigravity` as a configured usage provider for status-bar visibility, so a checked `Antigravity Usage` item renders a pending/error segment even before a fresh usage snapshot arrives.
- [ ] Include `antigravity` in the usage empty-state pending/configured checks.
- [ ] Include `antigravity: null` in the initial renderer `rateLimits` store state so the UI has a stable provider key before the first API push.
- [ ] Add a regression test covering the checked-menu-item versus visible-segment contract.

## Acceptance
Done when Orca 1.4.128+ shows the Antigravity usage segment whenever `Antigravity Usage` is enabled and the agent is available, including the pre-refresh/pending state, and the regression test passes.

## Updates
- **2026-07-08:** Local hotpatch restored the visualization by adding Antigravity to provider visibility/empty-state handling and initial rate-limit state. Verification: `node --test` regression against extracted packaged chunks passed locally after patching.