User GitLab Credits Dashboard - Engineering work behind a FF
## Summary
Engineering work to build the **self-scoped GitLab Credits usage view** for individual users, behind the feature flag `user_gitlab_credits_dashboard`.
Reuses the existing GitLab Credits dashboard data pipeline and UI components, scoped server-side to the current user, so any human group member (any role, including Guest) can see their own credit consumption within a top-level group — without Owner/Admin permissions.
**Parent epic:** End-user view of GitLab Credit Consumption (&21595)
**Source issue:** gitlab-org/gitlab#604722
## Scope
- **.com only** (SaaS). No Self-Managed/Dedicated.
- **Consumption-only.** The used/limit meter is deferred pending the spike gitlab-org/gitlab#605062.
- Everything behind the `user_gitlab_credits_dashboard` feature flag.
## Approach
- Add a per-user daily usage series in CustomersDot (dependency, deploy first).
- New self-scoped GraphQL field (`selfCreditsUsage`) hard-clamped to `current_user.id`, membership-gated (not Owner-gated), bypassing the `display_gitlab_credits_user_data` 404 guard.
- New Vue dashboard under `usage_quotas/user_credits_dashboard/`, reusing chart/filter components from `wallet_agnostic_credits_dashboard`.
- Personal entry point via `Profiles::GitlabCreditsDashboardController`.
## Issue breakdown
Small, incremental MRs. Backend/data first, then component-per-MR frontend, then entry point.
### Backend / data
1. CustomersDot: per-user `dailyUsage` field
2. GitLab: CDot client per-user daily usage method
3. GitLab: `selfCreditsUsage` GraphQL resolver + type + backend model
### Frontend (component-per-MR)
4. App shell + GraphQL wiring
5. Date range + product filters
6. Billing-period headline stat
7. Self usage cards (3 cards)
8. Credit consumption chart
9. Zero state
10. Blocked / at-or-over-limit state
### Entry point
11. `Profiles::GitlabCreditsDashboardController` + route + view
12. Personal menu entry
epic