5.2 Respect the requested trusted-session mode

[marwannettour]

Parent epic: #311

Summary

Apply JoinOnly, Inventory, and Synchronize behavior after a trusted session is accepted.

Requirements

• JoinOnly joins the session only.
• Inventory joins and starts inventory when authorized.
• Synchronize joins, starts inventory if needed, and starts synchronization when authorized.
• Check local policy or grants before any automatic action beyond join.

Acceptance criteria

• Modes map to the intended actions.
• Unauthorized modes are rejected or downgraded according to policy.
• Tests cover mode behavior.