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/_upload.html

@@ -2,13 +2,18 @@
   {% set pas = 1 %}{% include '_stepper.html' %}
   {# US-004 (3.6): bara de upload accentuata (border de accent) ca sa ramana punctul
      de intrare evident chiar cu tabelul Trimiteri lung dedesubt (D-1.1/D-5.2). #}
+  {% from '_eroare.html' import card_erori %}
   <div class="card" style="border-color:var(--accent);">
 
     {% if message %}
     <div class="flash" style="margin-bottom:12px;">{{ message }}</div>
     {% endif %}
 
-    {% if error %}
+    {% if eroare_upload %}
+    <div style="margin-bottom:12px;">
+      {{ card_erori([eroare_upload]) }}
+    </div>
+    {% elif error %}
     <div class="flash" style="border-color:var(--err); background:color-mix(in srgb, var(--err) 12%, var(--card)); margin-bottom:12px;"
          role="alert">{{ error }}</div>
     {% endif %}