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.

.gitignore

@@ -93,6 +93,12 @@ settings.local.json
 # Local agent/tooling metadata
 .agents/
 .codex/
+.claude/
+
+# Android packages and local SDK config
+*.apk
+*.aab
+local.properties
 
 # Fuzzing artifacts (tests/PalladiumWallet.Fuzz)
 findings/