Brief emotional-mix guardrails + source on its own line

Composition (Codex's priority — content mix was the louder problem):
- _select_diverse now guards the daily five's emotional tone: at most 1 health,
  at most 2 science+health combined, at most 2 of any topic, distinct sources —
  so at least three of the five are community/culture/animals/environment when
  available. Caps relax (mix, then source) only to fill on thin days.
- Verified live: today's five went to environment x2, health, animals, science.

UI:
- Source moved to its own line below the tags, left-justified, for uniform
  rhythm across hero and tiles (was sometimes trailing the tags, right-aligned).
- Watermark kept as-is (intentionally subtle; liked).

Tests updated for the emotional-mix contract (80 total).

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

frontend/src/lib/components/ArticleCard.svelte

@@ -36,8 +36,8 @@
     <div class="tags">
       {#if article.topic}<span class="tag">{article.topic}</span>{/if}
       {#if article.flavor}<span class="tag soft">{article.flavor}</span>{/if}
-      <span class="src">{article.source}</span>
     </div>
+    <div class="src">{article.source}</div>
 
     <h3><a href={safeHref} target="_blank" rel="noopener">{article.title}</a></h3>
 
@@ -85,7 +85,8 @@
     padding: 2px 9px; font-weight: 600; text-transform: capitalize;
   }
   .tag.soft { background: var(--sage-soft); color: var(--sage-deep); }
-  .src { color: var(--muted); margin-left: auto; }
+  /* Source on its own line below the tags, left-justified, for uniformity. */
+  .src { color: var(--muted); font-size: 0.78rem; margin: -2px 0 2px; }
 
   h3 { font-size: 1.18rem; }
   h3 a:hover { color: var(--sage-deep); }
@@ -134,7 +135,7 @@
     color: var(--sage); opacity: 0.05; text-transform: lowercase; letter-spacing: -0.02em;
     pointer-events: none; user-select: none;
   }
-  .tile .tags, .tile h3, .tile .why, .tile .actions { position: relative; }
+  .tile .tags, .tile .src, .tile h3, .tile .why, .tile .actions { position: relative; }
 
   /* ---- Hero WITH image: two columns, with an atmospheric overlay ---- */
   .hero { display: grid; grid-template-columns: 1.1fr 1fr; }