UX improvement: Inline editing for identity overrides in Edit Feature modal

## Problem

In the Edit Feature modal → Identity Overrides tab, clicking "Edit" opens a new browser tab navigating to the identity page. This breaks the user's flow — they lose context of the feature they were editing and have to navigate back.

I understand the intention of avoiding duplicated logic, since this approach keeps identity overrides editable in a single place. However, I thought it would still be worth raising the discussion.

## Proposed improvement

Replace the new-tab navigation with an inline expandable/accordion row within the same modal. Clicking "Edit" would expand the row to show:
- Enabled toggle
- Value editor (with format selector: .txt, .json, .xml, .toml, .yaml)
- Description field
- Save/Cancel buttons

This keeps the user in context and reduces the number of steps to edit an identity override.

**Location**: `web/components/modals/create-feature/index.js` lines 1496–1507

## Acceptance Criteria

- [ ] Clicking "Edit" expands the row inline instead of opening a new tab
- [ ] User can toggle enabled, edit value, and save without leaving the modal
- [ ] Expanded row collapses on save or cancel
- [ ] No regression on the identity page edit flow (direct navigation still works)