feat(fuzz): add SharpFuzz-based fuzzing for untrusted-input parsers

New tests/PalladiumWallet.Fuzz project: one target per parser that
consumes untrusted input (block headers, Merkle proofs, peer lists,
wallet files, user-pasted mnemonics/keys/addresses/amounts), each
encoding the parser's documented error contract - any exception beyond
that contract is a finding, reported as a crash.

Three ways to run: the seed corpus (with regression inputs for every
crash found so far, including the two fixed in prior commits) replays
automatically inside dotnet test via FuzzCorpusTests, so a fixed
contract violation can't silently return; a built-in random-mutation
mode needs no external tooling (dotnet run -- <target> --random N);
and fuzz.sh drives real coverage-guided campaigns via afl++ +
SharpFuzz instrumentation for pre-release or post-parser-change runs.

tests/PalladiumWallet.Fuzz/PalladiumWallet.Fuzz.csproj

@@ -0,0 +1,24 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+    <IsPackable>false</IsPackable>
+    <!-- Fuzzing wants stable, non-inlined instrumentation points. -->
+    <TieredCompilation>false</TieredCompilation>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="SharpFuzz" Version="2.3.0" />
+    <ProjectReference Include="..\..\src\Core\PalladiumWallet.Core.csproj" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <!-- Seed corpus travels next to the binary so replay and the regression
+         test in PalladiumWallet.Tests can find it via AppContext.BaseDirectory. -->
+    <None Include="Corpus\**\*" CopyToOutputDirectory="PreserveNewest" />
+  </ItemGroup>
+
+</Project>