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/announcement/api/src/main/kotlin/io/element/android/features/announcement/api/AnnouncementService.kt

@@ -12,15 +12,34 @@ import androidx.compose.runtime.Composable
 import androidx.compose.ui.Modifier
 import kotlinx.coroutines.flow.Flow
 
+/**
+ * Queues the full-screen announcements shown to the user once, such as the notice about a new feature.
+ *
+ * A dismissed announcement is remembered so it is not shown again.
+ */
 interface AnnouncementService {
+    /**
+     * Queues an announcement, unless the user has already dismissed it.
+     *
+     * @param announcement the announcement to show.
+     */
     suspend fun showAnnouncement(announcement: Announcement)
 
+    /**
+     * Records that the user dismissed an announcement, so it is not queued again.
+     *
+     * @param announcement the announcement that was dismissed.
+     */
     suspend fun onAnnouncementDismissed(announcement: Announcement)
 
+    /** The announcements still waiting to be shown, in the order they should appear. */
     fun announcementsToShowFlow(): Flow<List<Announcement>>
 
     /**
      * Use this composable to render the announcement UI in Fullscreen.
+     * Draws nothing while there is no announcement to show.
+     *
+     * @param modifier layout modifier for the container.
      */
     @Composable
     fun Render(