Port upstream 0.55.0: Gemini shutdown guidance

[Finesssee]

Summary

• port upstream CodexBar v0.55.0 Gemini consumer-tier shutdown detection from Detect Google's live Gemini consumer-tier shutdown response steipete/CodexBar#3139
• recognize Google's ineligibleTiers + UNSUPPORTED_CLIENT shutdown signal from loadCodeAssist
• surface Antigravity migration guidance instead of a bare quota error
• keep paid, Standard, and Workspace/hosted-domain accounts outside the consumer shutdown path

Upstream evidence

• target release: v0.55.0
• upstream commit: 90e6651cd / Detect Google's live Gemini consumer-tier shutdown response steipete/CodexBar#3139

Validation

• C:/Users/mac/.cargo/bin/cargo.exe test -p codexbar gemini -> 6 passed
• focused rustfmt on rust/src/providers/gemini/api.rs
• git diff --check -> pass

Scope

Ports the provider-side Windows behavior only. macOS-specific login alerts, Keychain handling, and AppKit actions are intentionally not copied.

[Finesssee]

Thermo-nuclear review

No material code-quality findings. The shutdown signal is modeled as provider-local parsed state plus a pure eligibility predicate, keeping paid/workspace exclusions out of the fetch orchestration and covered by focused tests.

Verdict: APPROVED.