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/js/locales/en.json

@@ -0,0 +1,76 @@
+{
+  "numpad": {
+    "title": "Numeric Keypad",
+    "clear": "Clear",
+    "submit": "Confirm",
+    "decimal": "Decimal",
+    "close": "Close"
+  },
+  "measurement": {
+    "pass": "Pass",
+    "warning": "Warning",
+    "fail": "Fail",
+    "value": "Value",
+    "next": "Next measurement"
+  },
+  "common": {
+    "loading": "Loading...",
+    "save": "Save",
+    "cancel": "Cancel",
+    "confirm": "Confirm",
+    "delete": "Delete",
+    "edit": "Edit",
+    "search": "Search...",
+    "noResults": "No results",
+    "close": "Close",
+    "error": "Error",
+    "success": "Success",
+    "warning": "Warning",
+    "info": "Info",
+    "page": "Page",
+    "of": "of",
+    "previous": "Previous",
+    "next": "Next"
+  },
+  "theme": {
+    "light": "Light",
+    "dark": "Dark",
+    "toggle": "Toggle theme"
+  },
+  "language": {
+    "switch": "Switch language",
+    "it": "Italian",
+    "en": "English"
+  },
+  "auth": {
+    "login": "Sign in to your account",
+    "username": "Username",
+    "password": "Password",
+    "signIn": "Sign In",
+    "invalidCredentials": "Invalid credentials",
+    "enterCredentials": "Enter username and password",
+    "forgotPassword": "Forgot password? Contact administrator",
+    "welcome": "Welcome, {name}!",
+    "logoutSuccess": "Logged out successfully",
+    "loginRequired": "Please log in to continue"
+  },
+  "nav": {
+    "measurements": "Measurements",
+    "recipes": "Recipes",
+    "statistics": "Statistics",
+    "admin": "Admin",
+    "users": "Users",
+    "settings": "Settings",
+    "profile": "Profile",
+    "logout": "Logout"
+  },
+  "profile": {
+    "title": "User Profile",
+    "displayName": "Display Name",
+    "language": "Language",
+    "theme": "Theme",
+    "roles": "Roles",
+    "saveChanges": "Save Changes",
+    "updateSuccess": "Profile updated successfully"
+  }
+}