fix: bake version into binary at build time

Instead of hacking around the version in the Node.js wrapper script,
properly pass the version at build time via SANDBOX_AGENT_VERSION env var.

Changes:
- build.rs: Generate version.rs with VERSION constant from env var
- main.rs: Use generated version constant for clap --version
- Dockerfiles: Accept SANDBOX_AGENT_VERSION as build arg
- build.sh: Pass version as second argument to Docker builds
- release.yaml: Pass version to build script during CI
- Remove version hack from sdks/cli/bin/sandbox-agent wrapper

The version is now baked into the binary during the release build,
ensuring --version reports the correct npm package version.

docker/release/linux-x86_64.Dockerfile

@@ -66,6 +66,10 @@ WORKDIR /build
 # Build for x86_64
 FROM base AS x86_64-builder
 
+# Accept version as build arg
+ARG SANDBOX_AGENT_VERSION
+ENV SANDBOX_AGENT_VERSION=${SANDBOX_AGENT_VERSION}
+
 # Set up OpenSSL for x86_64 musl target
 ENV SSL_VER=1.1.1w
 RUN wget https://www.openssl.org/source/openssl-$SSL_VER.tar.gz \