docs(admin): add NatSpec documentation for revoke_role

[codenerde]

Description

Add comprehensive NatSpec documentation for the revoke_role function in the admin access-control module.

The documentation covers:

• Summary: explains that only the admin can revoke roles and that un-granted pairs return RoleNotGranted instead of panicking
• Arguments section: documents env, role, and address parameters
• Errors section: documents AdminError::RoleNotGranted return
• Panics section: documents the three panic conditions (uninitialized contract, zero-address sentinel, unauthorized caller)
• Intra-doc links: uses backtick-linked references to grant_role, Role, and AdminError::RoleNotGranted

Related Issues

Closes BCPathway#491

Checklist

• Documentation is clear and accurate
• Linter/Formatter passes with 0 warnings
• Follows NatSpec standard
• All tests pass (19/19)