Restyle UI to match Mago4 and add invoicing, warehouse, scadenzario

Rework the demo into a faithful Mago4 look-and-feel and expand it with
core ERP modules modelled on the real Mago4 database schema.

UI (ispirata a Mago4):
- Blue header with logo/search/operation date, desktop-style window tabs
- White sidebar with coloured module icons (Anagrafiche, Vendite, Acquisti,
  Amministrazione, Logistica)
- Card-based module landing pages with breadcrumb + tab strip
- Document detail forms with left tabs, line grid and totals box

Fatturazione (InvoiceMng / MA_SaleDoc):
- Document types (Fattura Immediata, DDT, Nota di Credito, ProForma)
- Lines with discount/IVA, automatic taxable/tax/total computation
- Document states (draft -> printed -> issued / posted_to_inventory)

Magazzino (Inventory / MA_InventoryEntries + MA_InventoryReasons):
- Inventory movements with load/unload reasons (DebitCreditSign)
- Posting a movement actually updates item balances
- Causali and stock valuation pages

Amministrazione / Scadenzario (AP_AR / MA_PyblsRcvbls):
- Open items (receivables/payables) with due date, method, state
- Settle action closes the item and recomputes the cash forecast

Dashboard riprogettata (focus su scadenze e to-do):
- Overdue alert banner, KPI for overdue payables/receivables
- Upcoming deadlines table, prioritised "Cose da fare" action list
- 30-day cash-flow forecast and customer credit-limit check

Adds REST endpoints for invoices, movements, schedules and dashboard data.

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

templates/inventory_reasons.html

@@ -0,0 +1,46 @@
+{% extends "base.html" %}
+{% block title %}Causali di Magazzino - Mago4 Demo{% endblock %}
+{% block window_tabs %}<a href="/inventory-reasons" class="window-tab active"><i class="material-icons">rule</i> Causali</a>{% endblock %}
+
+{% block content %}
+<div class="module-bar">
+    <div class="module-title">Causali di Magazzino</div>
+    <div class="breadcrumb"><a href="/">Mago4</a><span class="sep">»</span><a href="/magazzino">Logistica</a><span class="sep">»</span><span class="current">Causali</span></div>
+</div>
+<div class="tab-strip">
+    <a href="/magazzino">Magazzino</a>
+    <a href="/inventory-movements">Movimenti</a>
+    <a href="/warehouse">Giacenze</a>
+    <a href="/inventory-reasons" class="active">Causali</a>
+</div>
+
+<div class="doc-toolbar">
+    <button class="tb-btn" title="Nuova causale" onclick="alert('Nuova causale (demo)')"><i class="material-icons">add_box</i></button>
+    <button class="tb-btn" title="Stampa"><i class="material-icons">print</i></button>
+</div>
+
+<div class="content-pad">
+    <div class="alert alert-info"><i class="material-icons">info</i> Le causali determinano se un movimento <b>carica</b> o <b>scarica</b> la giacenza (campo <span class="mono">DebitCreditSign</span> in Mago4).</div>
+
+    <div class="panel">
+        <div class="panel-header"><h3><i class="material-icons">rule</i> Elenco Causali</h3></div>
+        <table class="data-table">
+            <thead><tr><th>Codice</th><th>Descrizione</th><th class="text-center">Segno</th><th class="text-center">Numerazione Fiscale</th><th class="text-center">Aggiorna Giacenze</th></tr></thead>
+            <tbody>
+                {% for r in reasons %}
+                <tr>
+                    <td class="text-bold mono">{{ r.code }}</td>
+                    <td>{{ r.description }}</td>
+                    <td class="text-center">
+                        {% if r.sign.value == 'load' %}<span class="badge badge-load"><i class="material-icons">add</i> Carico (+)</span>
+                        {% else %}<span class="badge badge-unload"><i class="material-icons">remove</i> Scarico (−)</span>{% endif %}
+                    </td>
+                    <td class="text-center">{% if r.fiscal %}<i class="material-icons text-success">check_circle</i>{% else %}<i class="material-icons text-mute">remove</i>{% endif %}</td>
+                    <td class="text-center">{% if r.updates_balance %}<i class="material-icons text-success">check_circle</i>{% else %}<i class="material-icons text-mute">remove</i>{% endif %}</td>
+                </tr>
+                {% endfor %}
+            </tbody>
+        </table>
+    </div>
+</div>
+{% endblock %}