feat(ui): #15 U5 — web upload import (HTMX) drop→mapare→preview→confirma

Implementare completa U5 din plan-treapta2.md (sectiunea 13):

- _upload.html: drop zone + buton accesibil (a11y: drag nu e la tastatura),
  drag-and-drop JS, mesaj 'NU se trimite nimic pana confirmi',
  selector foi pt multi-sheet xlsx, stari eroare/mesaj
- _mapcoloane.html: formular mapare coloane cu .maprow/.mapcol.grow,
  sugestii fuzzy pre-selectate, etiichete <label> vizibile, sample values,
  format data configurabil
- _preview_import.html: tabel 6 stari, pills rezumat, filtre pe stare,
  .chk per-rand pe needs_review (D11), banner declarant .banner.warn
  direct deasupra input-ului N (D12), bara confirmare sticky,
  text 'dubla cu randul N' pe duplicate_in_file (D10 daltonism),
  link export CSV randuri esuate
- base.html: .s-needs_review (warn), .s-already_sent/.s-duplicate_in_file
  (muted), .drop-zone, .banner.warn, .sticky-bar, .htmx-indicator
- routes.py: rute /_import/upload/mapare-coloane/preview/reset/confirma;
  helper _web_compute_preview refoloseste _resolve_row_for_preview,
  _already_sent_lookup, _signature din import_router (fara a-l edita);
  commit ON CONFLICT DO NOTHING (TOCTOU); log atestare
- tests/test_import_ui.py: 15 teste (dashboard, upload, mapare, preview,
  confirmare N corect/gresit, reset, erori, multi-sheet, a11y D10/D11/D12)

279 teste total, 0 esecuri.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/web/templates/dashboard.html

@@ -1,6 +1,9 @@
 {% extends "base.html" %}
 {% block content %}
 
+<!-- Sectiunea de import fisier: stare initiala = drop zone; HTMX swapeaza in flow -->
+{% include '_upload.html' %}
+
 <div class="card banner {% if not blocked %}hidden{% endif %}"
      hx-get="/_fragments/banner" hx-trigger="every 15s" hx-swap="outerHTML">
   <strong>Atentie:</strong> {{ blocked }} submission-uri blocate (error / needs_data / needs_mapping).