## Summary
Adds inline editing of existing per-user and per-group chat usage limit
overrides from the Limits tab. Admins can now click Edit on any override
row to modify the spend limit in-place, using the same form used for
adding overrides.
## Changes
**Backend** (`coderd/chats_test.go`)
- Added `UpdateUserOverride` and `UpdateGroupOverride` test cases
covering the upsert-in-place behavior.
**Frontend** (3 component files + 2 story files)
- `LimitsTab.tsx`: Edit state management, mutual-exclusion between
user/group edit modes, and handlers that prefill the form from the
existing override.
- `GroupLimitsSection.tsx`: Edit button per row, read-only group
identity in edit mode, Save/Cancel actions, disable states during
pending operations.
- `UserOverridesSection.tsx`: Same pattern as groups — Edit button,
read-only user identity, Save/Cancel, proper disable states.
- New Storybook stories for both sections (Default, EmptyState,
AddForm, EditForm).
## UX behavior
- Clicking Edit opens the inline form with the current spend limit
prefilled and the entity shown as read-only.
- Save uses the existing PUT upsert endpoint (no new API surface).
- Cancel returns to normal list view with form state cleared.
- Edit modes are mutually exclusive — editing a user override closes
any open group form and vice versa.
- All buttons and inputs disable during pending mutations.
- Add and delete continue to work after editing.
Michael Suchacz
b8a5344c92