feat(webapp): Improve the Usage page billing panels (#4820)

UI-only update of the **Usage** page (`/orgs/…/settings/usage`). **No
logic or data changes**: the loader is byte-identical to `main` and the
usage-bar calculations are unchanged.

### What changed
- **Credits** and **Month-to-date** panels now sit in matching cards,
with the big `$value` and title on one baseline-aligned row and the
progress bar full-width beneath.
- Added a **Set / Update billing limit** link (to the existing Billing
limits page) on the Month-to-date panel.
- The two progress bars share the same height/corners; the Month-to-date
panel shrinks when there's no billing limit to show.
- Removed the progress-bar load animation.
- **Tasks**: moved the "dev environment runs are excluded…" note beside
the title and switched the empty state to the standard `TableBlankRow`.

<img width="3456" height="1364" alt="CleanShot 2026-08-28 at 15 37
52@2x"
src="https://github.com/user-attachments/assets/cb69ec33-1521-47d1-ba0a-51b8afd7eb00"
/>

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>