test: add ServerProbe tool and opt-in live server test

ServerProbe is a read-only conformance/health checker for Electrum
protocol servers (Fulcrum, ElectrumX): handshake/TLS, features and
genesis, header linkage, Merkle proof vs header root, fees, latency.
LiveServerTests runs it from dotnet test when PALLADIUM_TEST_SERVERS is
set. Also ignore .claude/, apk/aab and local.properties.

tests/PalladiumWallet.ServerProbe/PalladiumWallet.ServerProbe.csproj

@@ -0,0 +1,15 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+    <IsPackable>false</IsPackable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\src\Core\PalladiumWallet.Core.csproj" />
+  </ItemGroup>
+
+</Project>