feat(messaging-ui): import a channel's roster from the settings panel

Phase C of channel-roster import. Adds the optional addMembers(threadId, userIds)
adapter seam (+ BulkAddResult) and, in ConversationSettings, a '#' mode on the
existing Add-people box that lists the channels you belong to — public AND
private, since the source list is your own membership-scoped conversation list.

Picking a channel STAGES the import (reads its roster, diffs against who is
already here) and shows a confirm — 'Add 9 people from #design? (3 already here)'
— so an administrative action never fires on a stray click. The result line
reports added / already-a-member / failed. Absent addMembers => the affordance is
hidden entirely and '#' is just a search string.

Bumped to 0.1.8. SDK suite: 15 files / 78 tests green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

packages/iios-messaging-ui/src/adapters/mock.ts

@@ -1,6 +1,7 @@
 import type { MessagingAdapter } from '../adapter';
 import type {
   Attachment,
+  BulkAddResult,
   ChannelSummary,
   ChannelVisibility,
   Conversation,
@@ -168,6 +169,22 @@ export class MockAdapter implements MessagingAdapter {
     if (t && !t.participants.includes(userId)) t.participants = [...t.participants, userId];
   }
 
+  /** Bulk add, mirroring the live door: already-members come back as `skipped`, never re-added. */
+  async addMembers(threadId: string, userIds: string[]): Promise<BulkAddResult> {
+    const t = this.threads.get(threadId);
+    if (!t) return { added: [], skipped: [], failed: [...userIds] };
+    const added: string[] = [];
+    const skipped: string[] = [];
+    for (const id of [...new Set(userIds)]) {
+      if (t.participants.includes(id)) skipped.push(id);
+      else {
+        t.participants = [...t.participants, id];
+        added.push(id);
+      }
+    }
+    return { added, skipped, failed: [] };
+  }
+
   async removeMember(threadId: string, userId: string): Promise<void> {
     const t = this.threads.get(threadId);
     if (t) t.participants = t.participants.filter((p) => p !== userId);