Warn when "Custom" binding username claim becomes unsupported

[Patryk Mroczko (patmr7)]

No description provided.

[Copilot]

Pull request overview

This PR adds an admin warning when the “Binding username claim” configuration is set to “Custom” in a scenario where that option is no longer supported (Microsoft IdP types with local_o365 user sync enabled), and wires the validation into relevant settings updates.

Changes:

• Adds a new validation function to warn admins when an unsupported “Custom” binding username claim is configured.
• Triggers the validation when OIDC auth settings change and when local_o365 user sync settings are updated.
• Introduces a new English language string for the warning message.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
local/o365/settings.php	Adds an updated-callback to user sync settings to run the binding-claim validation after changes.
auth/oidc/lib.php	Adds the warning/validation function and invokes it during auth settings validation.
auth/oidc/lang/en/auth_oidc.php	Adds the warning text shown to admins.

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