RM-304: base claimer permissions on their support team instead of granting full access

[biast12]

RM-304

Description

When a ticket's claim settings restrict support from viewing or typing, claiming rebuilds the channel overwrites. In that rebuild the claimer was bundled in with the admins and given the full StandardPermissions set, ignoring whatever their support team's configured permissions allowed or denied.

Type of Change

• Bug fix
• New feature
• Breaking change

Testing

• Claim with restrictive claim settings and a team that denies Mention Everyone → the claimer's overwrite denies it, Send Messages allowed.
• Claim with a custom team → claimer gets that team's permissions, not the full set.
• Unclaim or switch-panel under KeepAccess where the claimer loses panel access → the claimer keeps their existing overwrite.

Checklist

• My code follows the style of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works