feat(tasks): show upgrade prompt for over-limit cloud task creation

[tatoalo]

Problem

creating a cloud task while over the usage limit showed a raw rate-limit error instead of an upgrade prompt, and the task was created anyway (orphaned state)

cloud_task_rate_limit_gating.mp4

Closes #2511

Changes

• pre-flight gate, before cloud task creation, refresh the team's usage and if over limit --> show the existing UsageLimitModal and block creation (no task/run created)
• graceful 429 handling
• added also CLOUD_TASK_USAGE_BLOCKED event (bucket + is_pro) emitted when the pre-flight blocks
• small cleanups w/ a shared withCloudUsageLimitCheck wrapper for the three cloud-run calls

Depends on BE's posthog#62110

[greptile-apps]

Prompt To Fix All With AI

Fix the following 2 code review issues. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 2
apps/code/src/renderer/features/billing/preflightCloudUsage.test.ts:59-101
The four test cases for `assertCloudUsageAvailable` are written as standalone `it` blocks but share the same function under test and differ only in the usage snapshot input and expected output/side-effects. The team standard is to always prefer parameterised tests. Collapsing the "allows / blocks / falls back / fails open" cases into a `it.each` table would make future scenarios trivial to add.

### Issue 2 of 2
apps/code/src/renderer/features/billing/preflightCloudUsage.ts:57-67
`isUsageExceeded` gates on `usage.is_rate_limited || burst.exceeded || sustained.exceeded`, but `usageLimitArgs` only inspects the two bucket flags. If the backend ever sets `is_rate_limited: true` with both bucket `exceeded` flags still false (e.g. a server-side safety valve), `usageLimitArgs` returns `undefined` and `show()` is called with no args — the modal opens with `bucket: null, resetAt: null`. The user sees the generic "Usage limit reached" title with no reset countdown. The `isPro` gap is covered by `useSeat()` in the modal, but the missing reset time could be confusing.

_{Reviews (1): Last reviewed commit: "feat(tasks): show upgrade prompt for ove..." | Re-trigger Greptile}

[greptile-apps]

Prompt To Fix All With AI

Fix the following 1 code review issue. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 1
apps/code/src/renderer/features/task-detail/service/service.ts:62-74
**Inbox callers show error toast alongside the usage-limit modal**

The backstop calls `assertCloudUsageAvailable()`, which already shows the modal, then returns `{ success: false, error: "Usage limit reached" }`. Any caller that doesn't recognise this sentinel will also show an error toast, so the user sees both. Concretely, `useDiscussReport.ts` shows `toast.error("Failed to start discussion", { description: "Usage limit reached" })` and `useCreatePrReport.ts` shows `toast.error("Failed to start PR task", ...)` in the same case — neither currently checks for `failedStep === "usage_limit"` or the error string.

Using `CLOUD_USAGE_LIMIT_ERROR_MESSAGE` as the backstop's `error` value (matching what `useTaskCreation.ts` already guards against) would let inbox callers apply the same suppression check.

_{Reviews (2): Last reviewed commit: "feat(tasks): show upgrade prompt for ove..." | Re-trigger Greptile}

[github-actions]

React Doctor found no issues in the changed files. 🎉

_{Reviewed by React Doctor for commit ef91239.}