Fix Cursor usage always reporting 0 under credit-based pricing (#7)

[leek]

Summary

Fixes #7 — the Cursor entry always shows 0 usage on accounts using Cursor's current credit/usage-based pricing.

CursorUsageProvider summed numRequests from the legacy https://www.cursor.com/api/usage endpoint. Cursor froze those per-model request counters at 0 when it moved to credit-based pricing in June 2025, so the provider reported 0 even for accounts with heavy, paid usage. (The Settings panel already noted "Credit-based pricing since June 2025" — the provider just never followed.)

What changed

• Read real usage from dashboard/get-aggregated-usage-events and report dollars spent this billing period (totalCostCents / 100) via the existing .dollars UsageUnit, which DetailPopoverView and UsageHistoryTabView already render.
• The legacy /api/usage call is kept only for startOfMonth (billing-period window + reset time).
• The dashboard endpoint enforces a CSRF origin check — without Origin: https://cursor.com it returns 403 {"error":"Invalid origin for state-changing request"} — so that header is now sent.
• CursorPlan exposes a USD allotment (monthlyUsageLimitUSD) instead of monthlyRequestEstimate; the Settings limit field is relabeled from "requests" to "USD" and the view-model wiring follows.
• Falls back to summing per-model aggregations[].totalCents if the server omits the top-level total, and to startOfCurrentMonthUTC() / firstOfNextMonthUTC() when startOfMonth is missing. Existing disk cache + cachedOrThrow behavior is preserved.

API reference

POST https://cursor.com/api/dashboard/get-aggregated-usage-events
Cookie: WorkosCursorSessionToken=<userId>::<jwt>
Origin: https://cursor.com            # required (CSRF) — 403 without it
Content-Type: application/json
{ "teamId": -1, "startDate": "<ms>", "endDate": "<ms>" }

200 -> { "aggregations": [ { "modelIntent": "...", "totalCents": 123.4, ... } ],
         "totalInputTokens": "...", "totalCostCents": 53285.77 }

Testing

• xcodebuild test -scheme AgentBar -destination 'platform=macOS' → 287 tests, 0 failures (1 pre-existing skip).
• CursorUsageProviderTests rewritten for the dollar metric: dollars-from-totalCostCents, aggregations-sum fallback, reset from startOfMonth, plan limit as total, and the required Origin header. The mock URL protocol now routes the legacy GET and aggregated POST to separate stubs.
• Verified live against a real Cursor account: legacy /api/usage returns numRequests: 0, while the aggregated endpoint returns the correct period spend.

Notes

• Per-plan USD allotments are estimates (Ultra ≈ 20× Pro); .custom lets users set their own. The displayed used value is exact from the API.
• The cursorMonthlyLimit default is now interpreted as USD; non-custom plans overwrite it on selection, so only a .custom user with a stale stored request count would need to re-enter it once.