Adds a collapsible "Sessions" section to the user profile card that
appears when cross-signing is active and the profile belongs to another
user. Each session shows a colour-coded shield (green = verified, yellow
= unverified) and a "Verify" button for unverified devices that
initiates the SAS emoji flow via crypto.requestDeviceVerification.
New hook useOtherUserDevices fetches the target user's device list via
crypto.getUserDeviceInfo and reacts to CryptoEvent.DevicesUpdated.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
