docs: document CsCheck property-based tests in README and CLAUDE.md

CLAUDE.md

@@ -40,7 +40,7 @@ by `MainWindow` on desktop and as the single-view root on Android.
 `export PATH="$HOME/.dotnet10:$PATH" DOTNET_ROOT="$HOME/.dotnet10"`.
 
 - Build: `dotnet build`
-- Tests (headless, the primary verification layer): `dotnet test` — single: `dotnet test --filter "FullyQualifiedName~TestName"`
+- Tests (headless, the primary verification layer): `dotnet test` — single: `dotnet test --filter "FullyQualifiedName~TestName"`; property-based tests (CsCheck, `PropertyTests.cs`) run in the same command and take ~30 s
 - GUI hot reload: `dotnet watch --project src/App.Desktop` (on WSL2/WSLg the window shows on the Windows desktop, no graphics dependencies to install)
 - CLI: `dotnet run --project src/Cli -- <command>` (no args → usage)
 - Windows publish: `dotnet publish src/App.Desktop -r win-x64 -p:PublishSingleFile=true --self-contained`

README.md

@@ -141,6 +141,8 @@ dotnet test tests/PalladiumWallet.Tests
 
 > Cross-implementation tests compare addresses, txids and PSBTs against reference golden vectors: a different address or txid is a blocking bug.
 
+The suite includes **property-based tests** ([CsCheck](https://github.com/AnthonyLloyd/CsCheck)) in `tests/PalladiumWallet.Tests/PropertyTests.cs`. These generate hundreds of random inputs per test and verify invariants that must hold universally — no crash on arbitrary strings, encrypt/decrypt roundtrip for any plaintext and password, every leaf in a randomly-built Merkle tree verifies against its root. They run automatically with `dotnet test` and take ~30 s.
+
 ---
 
 ## Building