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/Core/Spv/Scripthash.cs

@@ -4,8 +4,8 @@ using NBitcoin;
 namespace PalladiumWallet.Core.Spv;
 
 /// <summary>
-/// Scripthash del protocollo di indicizzazione (blueprint §0/§10): SHA-256
-/// dello scriptPubKey con i byte in ordine inverso, esadecimale.
+/// Script hash for the indexing protocol (blueprint §0/§10): SHA-256 of the
+/// scriptPubKey with bytes reversed, encoded as lowercase hex.
 /// </summary>
 public static class Scripthash
 {