Add KDoc to the single-interface feature API modules

Cover the last remaining interfaces across features/announcement, cachecleaner,
call, contentscanner, createroom, knockrequests, lockscreen, rolesandpermissions,
startchat, userprofile and viewfolder, with their members and parameters.

Grouped into one commit rather than eleven near-empty ones, per the AGENTS.md rule
about tiny commits.

This completes every features/* api module.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

features/call/api/src/main/kotlin/io/element/android/features/call/api/CurrentCallService.kt

@@ -10,6 +10,9 @@ package io.element.android.features.call.api
 
 import kotlinx.coroutines.flow.StateFlow
 
+/**
+ * Tracks the call the user is currently in on this device, so unrelated parts of the app can react to it.
+ */
 interface CurrentCallService {
     /**
      * The current call state flow, which will be updated when the active call changes.