PR 3 : feat(admin): add email template editor

[Gurnoor123kaushal]

Completed the Email Template Editor task.

Added a dedicated Email Templates page in the Admin Panel.
Added mock persistence using localStorage.
Added support for predefined template variables.
Added subject and email body editing.
Added template preview with sample data.
Added save functionality with validation.
Added the Email Templates route and sidebar navigation.

[Krisha190235]

The email template editor (AP‑040) looks good, but this can't merge yet — it's 40 behind main and reverts/collides with recently merged work: Roles.test.jsx is back on 3/4 permissions (main is 7/8, so it'd fail), and it re‑adds the getDashboardMetrics dashboard‑test fix that already landed via #644 (hence the AdminDashboard conflicts). Please rebase onto current main, keep main's Roles.test and AdminDashboard.test/AdminDashboard.jsx, and re‑apply just the Email Templates page + the sidebar nav and route. The sidebar's fine otherwise (it keeps all current items and adds Email Template).

[Krisha190235]

Rebased onto current main and reduced to the Email Templates feature only. Dropped the stale bits it was dragging — the AdminDashboard.jsx and rolesAPI.js changes were just prettier reformatting, and it was reverting the AdminDashboard ellipsis + Roles counts — so those are back to main. Re‑applied just the Email Templates page (mock‑backed), the sidebar nav item and the route. Net diff is 4 files; eslint clean, full admin suite green (19 suites / 72 tests), build passes. Force‑pushed to update in place. 🙏