## Description
Adds the `GET /api/v2/users/{user}/ai/spend` endpoint returning the
user's current AI spend, effective budget, and period bounds.
## Changes
- Add `userAISpendStatus` handler under the same feature/experiment gate
as `/api/v2/users/{user}/ai/budget`.
- Add `codersdk.UserAIBudgetSummary` (embedded into `UserAISpendStatus`)
and a `UserAISpendStatus` client method.
- Move `LimitSource` from `coderd/aibridge/budget` to `codersdk` so the
type is shared across endpoints.
Closes https://linear.app/codercom/issue/AIGOV-472
> [!NOTE]
> Initially generated by Claude Opus 4.7, modified and reviewed by
@ssncferreira
Susana Ferreira
48f07e6e13