feat(landing): fragment wizard import in loc de sectiunea 'calculator' + preturi pe 3 planuri

- sectiunea 'Cum functioneaza': mockup al wizard-ului real (stepper 4 pasi,
  incarcare, potrivire coloane, verificare cu stari si sugestie preselectata,
  bara de confirmare 'Trimite la RAR')
- carduri pret: chips canal de intrare (CSV/XLSX vs +API), banda de economie
  lunara, liste compacte 'Tot ce este la X +'
- cardul Premium eliminat din grila si din select-ul de plan (landing + /signup);
  tier-ul 'premium' ramane valid in backend, alocat doar de admin

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

app/web/templates/signup.html

@@ -44,8 +44,8 @@
   {% endif %}
 
   {# Format aliniat la formularul de inregistrare din landing (#inregistrare): aceleasi campuri,
-     etichete, placeholder-uri si stil. Valorile `plan` = coduri tier (free/standard/pro/premium),
-     normalizate server-side. #}
+     etichete, placeholder-uri si stil. Valorile `plan` = coduri tier (free/standard/pro),
+     normalizate server-side; 'premium' ramane valid in backend, doar alocat de admin. #}
   <form method="post" action="/signup">
     <input type="hidden" name="csrf_token" value="{{ csrf_token }}">
     <label style="display:block;margin-bottom:14px;">
@@ -75,7 +75,6 @@
         <option value="free"{% if not plan or plan == 'free' %} selected{% endif %}>Gratuit — 0 lei/lună</option>
         <option value="standard"{% if plan == 'standard' %} selected{% endif %}>Standard — 49 lei/lună</option>
         <option value="pro"{% if plan == 'pro' %} selected{% endif %}>Pro — 59 lei/lună</option>
-        <option value="premium"{% if plan == 'premium' %} selected{% endif %}>Premium — la cerere</option>
       </select>
     </label>
     <label style="display:flex;gap:9px;align-items:flex-start;margin-bottom:18px;font:400 13px/1.5 var(--font-ui);color:var(--muted);cursor:pointer;">