feat(errors): erori pe 3 niveluri (problema+cauza+fix) pe API si UI (PRD 5.4)

Catalog central pur app/errors.py ca sursa unica cod->{problema,fix},
consumat de API+UI+worker. Aditiv (field/message pastrate la octet) +
rar_error stocat superset. Scope: fluxul de declarare; login/signup/CSRF
neatinse. labels.parse_erori degradeaza gratios; UI progresiv AA light+dark.
631 teste.

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

app/web/templates/_trimitere_detaliu.html

@@ -1,3 +1,4 @@
+{% from "_eroare.html" import card_erori %}
 <div class="card" id="detaliu-card-{{ id }}" style="border-color:var(--accent);">
   <div style="display:flex; align-items:center; gap:8px; flex-wrap:wrap; margin:0 0 12px;">
     <h2 style="font-size:15px; margin:0;">Detaliu trimitere #{{ id }}</h2>
@@ -27,7 +28,11 @@
     <div><div class="muted" style="font-size:12px;">Urmatoarea incercare</div><div>{{ next_attempt_at }}</div></div>
   </div>
 
-  {% if motiv %}
+  {% if erori_3n %}
+  <div style="margin-top:12px; padding-top:10px; border-top:1px solid var(--line);">
+    {{ card_erori(erori_3n) }}
+  </div>
+  {% elif motiv %}
   <div style="margin-top:12px; padding-top:10px; border-top:1px solid var(--line);">
     <div class="muted" style="font-size:12px;">Motiv</div>
     <div>{{ motiv }}</div>