add admin edit privileges for empl directory

[mia-oww]

This PR changes employee directory admin permissions, by allowing users with admin privilege to edit other employee profiles in the directory. Previously, only users could edit their own profile, with no special admin permissions.

[Thomasbenissan]

Overall looks great! A couple things to note:

This PR was based on an older version of EmployeeDirectory that took userId, username, userRole, and userMetadata as props. After PR #72 merged, the component was refactored to only take id and fetch employee data from the backend API.

So I just went in and made a couple fixes:

Merged main into this branch and resolved the conflict in EmployeeDirectory.tsx
Kept the new backend-driven data fetching from main, added isAdmin as a clean separate prop instead of deriving it from the old userMetadata prop
Updated page.tsx to pass isAdmin={data.is_admin ?? false} from the already-fetched user metadata
SidePanel and ProfileTile admin logic (the core contribution of this PR) was preserved as-is
The canEdit = isCurrentUser || isAdmin logic in ProfileTile and the Admin badge display work correctly with the updated component structure.

Again, good work!