Add ViewFamilyChildren permission for need-to-know child visibility

[Copilot]

Children in a family should only be visible on a need-to-know basis. Families/community members serving other families should not see co-assigned families' children by default.

Changes

• Permission.cs — New ViewFamilyChildren = 160 enum value in the FamilyAndPersonInfo section
• AuthorizationEngine.cs — DiscloseFamily() returns empty children list when permission is absent, enforced at the disclosure layer:

  Children = contextPermissions.Contains(Permission.ViewFamilyChildren)
      ? family.Children.Select(child => DisclosePerson(child, contextPermissions)).ToImmutableList()
      : ImmutableList<Person>.Empty,

• GeneratedClient.ts — Frontend enum kept in sync
• groupedPermissions.tsx — Added to FamilyAndPersonInfo category in role configuration UI
• FamilyScreen.tsx — Child cards and "Add Child" button gated behind the permission

[LarsKemmann]

@PabloDinella Can you please review and plan to merge this? The only challenge is that we will require a permissions update for every organization when this is launched to add the View Family Children permission to every role that currently has View Person Contact Info. I think that's the most appropriate way to make this backwards compatible (the only other option I came up with is that we could add a permissions schema version to each config.json file and use that to make automatic edits to the files on read -- but that might be a bit too complicated to just build right now without proper design).