Rework history: opened + replaced only, with per-item removal

History was logging every article merely displayed, which made it noise. Split
the two concepts cleanly:
- "displayed" (seenIds) still tracks everything shown, but only to stop Replace
  recycling stories — it no longer feeds history.
- "history" now records only deliberate events: articles the user OPENED (card
  click) or ones they REPLACED away (recoverable accidental swaps).

Also: per-item removal (× in the History panel; DELETE /api/history/{id}), and
when signed in the panel shows the account (cross-device) history. First-sign-in
import now folds the meaningful history (not everything shown). Copy updated.
115 tests pass.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/lib/components/ArticleCard.svelte

@@ -1,7 +1,7 @@
 <script>
   import { auth, savedIds, toggleSave } from '$lib/auth.svelte.js';
 
-  let { article, onaction, onreplace, ontag, onimageerror, hero = false } = $props();
+  let { article, onaction, onreplace, ontag, onimageerror, onview, hero = false } = $props();
   let isSaved = $derived(savedIds.has(article.id));
 
   const humanize = (s) => (s || '').replace(/-/g, ' ');
@@ -50,7 +50,7 @@
   data-topic={article.topic ?? ''}
 >
   {#if showImage}
-    <a class="media" href={safeHref} target="_blank" rel="noopener">
+    <a class="media" href={safeHref} target="_blank" rel="noopener" onclick={() => onview?.(article)}>
       <img src={article.image_url} alt="" loading="lazy" referrerpolicy="no-referrer"
            onerror={() => { failed = true; onimageerror?.(); }} />
     </a>
@@ -71,7 +71,7 @@
     </div>
     <div class="src">{article.source}</div>
 
-    <h3><a href={safeHref} target="_blank" rel="noopener">{article.title}</a></h3>
+    <h3><a href={safeHref} target="_blank" rel="noopener" onclick={() => onview?.(article)}>{article.title}</a></h3>
 
     {#if hero && article.description}
       <p class="desc">{article.description}</p>