Add pagination support for admin users list endpoint

[JohnRDOrazio]

Description

The GET /admin/users endpoint currently uses a default limit of 100 users for both listProjectUsers() and listAllUsers() calls. With more than 100 users, results will be silently truncated.

Suggested Enhancement

• Accept limit and offset query parameters
• Return pagination metadata (total count, current page, etc.)
• Consider auto-pagination to fetch all pages if no limit is specified

Files Affected

• src/Handlers/Admin/UsersHandler.php
• src/Services/ZitadelService.php (methods already support limit/offset)

Priority

Low - current limit of 100 is sufficient for the expected user base.

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Identified by CodeRabbit code review.