fix(clients): align client version constants to package manifests (CLI-18/21/26/29)

- .NET: add explicit <Version>0.1.2</Version> to client csproj (CLI-18)
- Go: ClientVersion 0.1.0-dev -> 0.1.2 (CLI-21)
- Python: __version__ 0.1.0 -> 0.1.2 to match pyproject.toml (CLI-26)
- Rust: CLIENT_VERSION now sourced from env!(CARGO_PKG_VERSION) so it
  cannot drift from Cargo.toml (CLI-29)

Verified: dotnet build clean; go build/test ok; cargo check/test/clippy
clean; pytest 127 passed. P2 client version-drift cluster.

Claude-Session: https://claude.ai/code/session_01DMXXvNuPekkkrTEyPNxEkW

clients/dotnet/ZB.MOM.WW.MxGateway.Client/ZB.MOM.WW.MxGateway.Client.csproj

@@ -19,6 +19,7 @@
   <PropertyGroup>
     <IsPackable>true</IsPackable>
     <PackageId>ZB.MOM.WW.MxGateway.Client</PackageId>
+    <Version>0.1.2</Version>
     <Description>.NET 10 gRPC client for the MxAccessGateway service. Provides typed wrappers, retry, and a lazy-browse walker over the Galaxy Repository hierarchy.</Description>
     <PackageReadmeFile>README.md</PackageReadmeFile>
     <!-- Only the shipped library generates XML docs (matching src/Contracts). The Cli and