feat: FASE 2 - Client Base (layout, login, navbar, tema, i18n)

Implementazione completa del frontend Flask:
- Layout base.html con TailwindCSS CDN, dark/light theme, flash messages
- Navbar responsive role-based (Maker, MeasurementTec, Metrologist, Admin)
- Login page professionale con form + API integration
- Profilo utente: nome, lingua, tema, badge ruoli
- Sistema tema dark/light: CSS variables + Alpine.js store + localStorage
- i18n completo IT/EN: Flask-Babel (.po) + alpinejs-i18n (JSON)
- API Client riscritto: error handling normalizzato, no crash su 4xx/5xx
- CSRF protection con Flask-WTF su tutti i form
- Logo aziendale dinamico da system_settings
- Asset SVG: tmflow-logo.svg + tmflow-icon.svg (favicon)

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

client/static/img/tmflow-icon.svg

@@ -0,0 +1,27 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 32 32" fill="none">
+  <!-- Stylized Caliper Icon for Favicon -->
+
+  <!-- Caliper outer frame -->
+  <rect x="2" y="3" width="5" height="26" rx="1.5" fill="#2563EB"/>
+  <rect x="2" y="3" width="19" height="5" rx="1.5" fill="#2563EB"/>
+  <rect x="2" y="24" width="19" height="5" rx="1.5" fill="#2563EB"/>
+
+  <!-- Sliding jaw -->
+  <rect x="12" y="8" width="4.5" height="6.5" rx="1" fill="#1E40AF"/>
+  <rect x="12" y="17.5" width="4.5" height="6.5" rx="1" fill="#1E40AF"/>
+
+  <!-- Depth rod -->
+  <rect x="4" y="14" width="12" height="3.5" rx="1" fill="#3B82F6" opacity="0.55"/>
+
+  <!-- Scale markings -->
+  <rect x="8" y="5" width="1" height="2.5" rx="0.5" fill="#FFFFFF" opacity="0.65"/>
+  <rect x="11" y="5" width="1" height="2.5" rx="0.5" fill="#FFFFFF" opacity="0.65"/>
+  <rect x="14" y="5" width="1" height="2.5" rx="0.5" fill="#FFFFFF" opacity="0.65"/>
+  <rect x="17" y="5" width="1" height="2.5" rx="0.5" fill="#FFFFFF" opacity="0.65"/>
+
+  <!-- Flow arrow -->
+  <path d="M22 16 C25 16, 26.5 11, 29 11"
+        stroke="#3B82F6" stroke-width="2.2" stroke-linecap="round" fill="none"/>
+  <path d="M27 8.5 L29.5 11 L27 13.5"
+        stroke="#3B82F6" stroke-width="1.8" stroke-linecap="round" stroke-linejoin="round" fill="none"/>
+</svg>