Vouch request: Add Umans usage provider (/usage, omp usage, TUI status bar)

[hpost]

Umans is already a registered model + auth provider, but it is missing from the usage subsystem — so it does not appear in /usage, omp usage, or the TUI status bar footer.

I have implemented a UsageProvider for it (packages/ai/src/usage/umans.ts) that:

• Fetches GET https://api.code.umans.ai/v1/usage with Authorization: Bearer <api-key>
• Maps the rolling 5h request window + instantaneous concurrency limit onto the shared UsageReport shape
• Surfaces priority.low (burst deprioritization) as a provider note
• Sets window.id = "5h" so the status-line usage segment recognizes it (matches the existing "5h"/"7d" window-id contract)
• Leaves window.resetsAt undefined (rolling window — no single reset timestamp), following the zai precedent

Wired into DEFAULT_USAGE_PROVIDERS in auth-storage.ts (import + array entry, 2 lines). Includes a bun:test suite (8 tests) covering happy-path parse, base-URL override, non-ok response, wrong provider/credential rejection, priority-low note, and the rolling-window no-resetsAt invariant.

bun check passes, full packages/ai suite green (2486 pass, 0 fail), live E2E verified against the real endpoint.

Branch: hpost/oh-my-pi:umans-usage-provider

Would appreciate a vouch to open the PR.

[can1357]

!vouch @hpost
Done!