docs: translate all code comments to English (language policy)

Translate every Italian /// XML doc comment, <!-- --> XAML comment, and
// inline comment to English across all source files (Core, App, tests).
Add the language policy to CLAUDE.md (conversation Italian; all code
and docs English). Update one test assertion that checked an Italian
exception message that was also translated.

src/App/Styles/Theme.axaml

@@ -1,34 +1,34 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
     <!-- ============================================================
-         Design token del wallet Palladium.
-         Identità: blu cobalto (fiducia) + verde (denaro/positivo),
-         derivati dal logo. Stile "fintech pulito".
+         Palladium wallet design tokens.
+         Identity: cobalt blue (trust) + green (money/positive),
+         derived from the logo. "Clean fintech" style.
 
-         Tutti i colori sono SEMANTICI (ruolo, non nome): i componenti
-         non devono mai usare hex inline ma questi brush. Definiti per
-         entrambe le varianti (chiaro/scuro) via ThemeDictionaries, così
-         l'app segue il tema di sistema senza ulteriore configurazione.
+         All colors are SEMANTIC (role, not name): components
+         must never use inline hex but these brushes. Defined for
+         both variants (light/dark) via ThemeDictionaries, so
+         the app follows the system theme with no further configuration.
          ============================================================ -->
 
     <ResourceDictionary.ThemeDictionaries>
 
-        <!-- ============ TEMA CHIARO ============ -->
+        <!-- ============ LIGHT THEME ============ -->
         <ResourceDictionary x:Key="Light">
-            <!-- Superfici -->
+            <!-- Surfaces -->
             <SolidColorBrush x:Key="AppBackgroundBrush" Color="#F1F5F9"/>     <!-- slate-100 -->
             <SolidColorBrush x:Key="SurfaceBrush"        Color="#FFFFFF"/>
             <SolidColorBrush x:Key="SurfaceAltBrush"     Color="#F8FAFC"/>     <!-- slate-50 -->
             <SolidColorBrush x:Key="OverlayCardBrush"    Color="#FFFFFF"/>
             <SolidColorBrush x:Key="ScrimBrush"          Color="#66000000"/>   <!-- 40% -->
-            <!-- Bordi e separatori -->
+            <!-- Borders and separators -->
             <SolidColorBrush x:Key="BorderSubtleBrush"   Color="#E2E8F0"/>     <!-- slate-200 -->
             <SolidColorBrush x:Key="BorderStrongBrush"   Color="#CBD5E1"/>     <!-- slate-300 -->
-            <!-- Testo -->
+            <!-- Text -->
             <SolidColorBrush x:Key="TextPrimaryBrush"    Color="#0F172A"/>     <!-- slate-900 -->
             <SolidColorBrush x:Key="TextSecondaryBrush"  Color="#475569"/>     <!-- slate-600 -->
             <SolidColorBrush x:Key="TextMutedBrush"      Color="#94A3B8"/>     <!-- slate-400 -->
-            <!-- Brand / stato -->
+            <!-- Brand / state -->
             <SolidColorBrush x:Key="PrimaryBrush"        Color="#2563EB"/>     <!-- blue-600 -->
             <SolidColorBrush x:Key="PrimaryHoverBrush"   Color="#1D4ED8"/>     <!-- blue-700 -->
             <SolidColorBrush x:Key="OnPrimaryBrush"      Color="#FFFFFF"/>
@@ -36,29 +36,29 @@
             <SolidColorBrush x:Key="SuccessBrush"        Color="#16A34A"/>     <!-- green-600 -->
             <SolidColorBrush x:Key="WarningBrush"        Color="#D97706"/>     <!-- amber-600 -->
             <SolidColorBrush x:Key="DangerBrush"         Color="#DC2626"/>     <!-- red-600 -->
-            <!-- Gradiente hero della card saldo: blu → indaco -->
+            <!-- Hero gradient of the balance card: blue → indigo -->
             <LinearGradientBrush x:Key="BalanceGradientBrush" StartPoint="0%,0%" EndPoint="100%,100%">
                 <GradientStop Offset="0" Color="#2563EB"/>
                 <GradientStop Offset="1" Color="#4F46E5"/>
             </LinearGradientBrush>
         </ResourceDictionary>
 
-        <!-- ============ TEMA SCURO ============ -->
+        <!-- ============ DARK THEME ============ -->
         <ResourceDictionary x:Key="Dark">
-            <!-- Superfici -->
+            <!-- Surfaces -->
             <SolidColorBrush x:Key="AppBackgroundBrush" Color="#0F172A"/>      <!-- slate-900 -->
             <SolidColorBrush x:Key="SurfaceBrush"        Color="#1E293B"/>     <!-- slate-800 -->
             <SolidColorBrush x:Key="SurfaceAltBrush"     Color="#273449"/>
             <SolidColorBrush x:Key="OverlayCardBrush"    Color="#1E293B"/>
             <SolidColorBrush x:Key="ScrimBrush"          Color="#99000000"/>   <!-- 60% -->
-            <!-- Bordi e separatori -->
+            <!-- Borders and separators -->
             <SolidColorBrush x:Key="BorderSubtleBrush"   Color="#334155"/>     <!-- slate-700 -->
             <SolidColorBrush x:Key="BorderStrongBrush"   Color="#475569"/>     <!-- slate-600 -->
-            <!-- Testo -->
+            <!-- Text -->
             <SolidColorBrush x:Key="TextPrimaryBrush"    Color="#F8FAFC"/>     <!-- slate-50 -->
             <SolidColorBrush x:Key="TextSecondaryBrush"  Color="#94A3B8"/>     <!-- slate-400 -->
             <SolidColorBrush x:Key="TextMutedBrush"      Color="#64748B"/>     <!-- slate-500 -->
-            <!-- Brand / stato (toni più luminosi su fondo scuro) -->
+            <!-- Brand / state (brighter tones on dark background) -->
             <SolidColorBrush x:Key="PrimaryBrush"        Color="#3B82F6"/>     <!-- blue-500 -->
             <SolidColorBrush x:Key="PrimaryHoverBrush"   Color="#60A5FA"/>     <!-- blue-400 -->
             <SolidColorBrush x:Key="OnPrimaryBrush"      Color="#0B1120"/>
@@ -66,7 +66,7 @@
             <SolidColorBrush x:Key="SuccessBrush"        Color="#22C55E"/>     <!-- green-500 -->
             <SolidColorBrush x:Key="WarningBrush"        Color="#F59E0B"/>     <!-- amber-500 -->
             <SolidColorBrush x:Key="DangerBrush"         Color="#EF4444"/>     <!-- red-500 -->
-            <!-- Gradiente hero della card saldo: blu → indaco (toni più profondi) -->
+            <!-- Hero gradient of the balance card: blue → indigo (deeper tones) -->
             <LinearGradientBrush x:Key="BalanceGradientBrush" StartPoint="0%,0%" EndPoint="100%,100%">
                 <GradientStop Offset="0" Color="#1D4ED8"/>
                 <GradientStop Offset="1" Color="#4338CA"/>
@@ -76,10 +76,10 @@
     </ResourceDictionary.ThemeDictionaries>
 
     <!-- ============================================================
-         Override dell'accento Fluent → blu del brand. Recolora in modo
-         coerente i controlli che leggono SystemAccentColor (bottoni
-         accent, selezioni, indicatore tab, focus) senza ritemplare nulla.
-         Indipendente dalla variante: #2563EB funziona su chiaro e scuro.
+         Override of the Fluent accent → brand blue. Recolors
+         consistently the controls that read SystemAccentColor (accent
+         buttons, selections, tab indicator, focus) without retemplating anything.
+         Variant-independent: #2563EB works on light and dark.
          ============================================================ -->
     <Color x:Key="SystemAccentColor">#2563EB</Color>
     <Color x:Key="SystemAccentColorDark1">#1D4ED8</Color>
@@ -89,8 +89,8 @@
     <Color x:Key="SystemAccentColorLight2">#60A5FA</Color>
     <Color x:Key="SystemAccentColorLight3">#93C5FD</Color>
 
-    <!-- Raggi globali dei controlli Fluent: arrotonda bottoni, input, combo,
-         liste in modo uniforme senza dover ritemplare ogni controllo. -->
+    <!-- Global Fluent control corner radii: rounds buttons, inputs, combos,
+         and lists uniformly without retemplating each control. -->
     <CornerRadius x:Key="ControlCornerRadius">8</CornerRadius>
     <CornerRadius x:Key="OverlayCornerRadius">12</CornerRadius>
 </ResourceDictionary>