4.8 Implement the local invitation acceptance policy

[marwannettour]

Parent epic: #310

Summary

Decide whether a validated invitation should be rejected, shown to the user, or auto-accepted.

Requirements

• Create a service such as ITrustedSessionInviteAcceptancePolicy.
• Check existing grants.
• Verify that the requested mode is allowed.
• Return a decision such as Reject, AskUser, or AutoAccept.
• Handle expired or revoked grants.

Acceptance criteria

• Invitations without a valid grant ask for user confirmation by default.
• Insufficient grants do not allow stronger requested modes.
• Expired or revoked grants are ignored.