v6 Phase C: Cookbook diversifiziert + 'Beste Wahl' hervorgehoben

- recipes.py: best-in-class je Use-Case, herstelleruebergreifend (Qwen3-Coder, Gemma 3,
  Mistral Small, DeepSeek-R1, Qwen3-VL) + neue Kategorie 'Nachdenken & Logik'.
- recipes-Endpoint: recommended_id = reichstes Setup das komplett passt.
- cookbook.js + CSS: 'Beste Wahl fuer dein System' (Rahmen + Badge).

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

static/css/components.css

@@ -216,5 +216,7 @@ button:disabled{opacity:.5;cursor:not-allowed}
   border-radius:var(--radius);padding:var(--sp-3) var(--sp-4);cursor:pointer;transition:border-color .15s,background .15s;
   color:var(--tx);font-family:var(--sans)}
 .card-btn:hover,.card-btn:focus{border-color:var(--accent);background:var(--bg2);outline:none}
+.card-btn.cb-best{border:2px solid var(--accent);background:rgba(45,212,191,.05)}
+.cb-best-tag{display:inline-block;font-size:11px;color:var(--accent-ink);background:var(--accent);border-radius:6px;padding:2px 9px;margin-bottom:8px;font-weight:500}
 .card-btn h3{margin:0;font-size:var(--text-lg);font-weight:500}
 .card-btn p{margin:var(--sp-2) 0 0;font-size:var(--text-sm);color:var(--mut)}