fix(thread): count user id tooltips from thread data

Replace the DOM-based user ID tooltip count with a deduped per-thread author map in `getThreadPostCountsByAuthor()`. This keeps mounted preview copies from doubling ID totals on desktop and mobile thread views.

src/lib/utils/__tests__/author-post-counts.test.ts

@@ -0,0 +1,39 @@
+import { describe, expect, it } from 'vitest';
+import { getThreadPostCountsByAuthor } from '../author-post-counts';
+
+describe('getThreadPostCountsByAuthor', () => {
+  it('counts the OP and replies per author short address', () => {
+    const post = { cid: 'post-1', author: { shortAddress: 'author-a' } } as any;
+    const replies = [
+      { cid: 'reply-1', author: { shortAddress: 'author-b' } },
+      { cid: 'reply-2', author: { shortAddress: 'author-a' } },
+      { cid: 'reply-3', author: { shortAddress: 'author-a' } },
+    ] as any[];
+
+    const counts = getThreadPostCountsByAuthor(post, replies);
+
+    expect(counts.get('author-a')).toBe(3);
+    expect(counts.get('author-b')).toBe(1);
+  });
+
+  it('deduplicates repeated CIDs so preview copies do not inflate the count', () => {
+    const post = { cid: 'post-1', author: { shortAddress: 'author-a' } } as any;
+    const duplicateReply = { cid: 'reply-1', author: { shortAddress: 'author-b' } } as any;
+    const replies = [duplicateReply, duplicateReply, { cid: 'reply-2', author: { shortAddress: 'author-b' } }] as any[];
+
+    const counts = getThreadPostCountsByAuthor(post, replies);
+
+    expect(counts.get('author-a')).toBe(1);
+    expect(counts.get('author-b')).toBe(2);
+  });
+
+  it('skips comments missing a cid or short address', () => {
+    const counts = getThreadPostCountsByAuthor(
+      { cid: 'post-1', author: { shortAddress: 'author-a' } } as any,
+      [{ cid: 'reply-1' }, { author: { shortAddress: 'author-b' } }] as any[],
+    );
+
+    expect(counts.get('author-a')).toBe(1);
+    expect(counts.has('author-b')).toBe(false);
+  });
+});