[harsheenkohli]

Summary

• Adds a "Remove All Identities" button to the Set Custom Identity screen of the test app
• Button calls Identity.removeAllIdentities() so the feature can be exercised manually

Stacked on feature/remove-all-identities.

Test plan

• Set a custom identity, confirm it appears alongside ECID in View Identities
• Tap Remove All Identities, confirm the custom namespace is removed and ECID is retained