Implement vendored OpenSSL for reliable cross-compilation

- Add openssl with vendored feature to workspace dependencies
- Include openssl in ck-embed to ensure vendored build
- Replace libssl-dev with build-essential for compiling vendored OpenSSL
- Set proper cross-compilation environment variables for ARM64
- This eliminates all system OpenSSL dependencies and pkg-config issues

Vendored OpenSSL compiles from source, avoiding the complex
cross-compilation issues with system OpenSSL libraries.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Fix OpenSSL cross-compilation for ARM64 Linux builds

- Enable multiarch for ARM64 packages in Ubuntu CI environment
- Install libssl-dev:arm64 for cross-compilation support
- Set proper OpenSSL environment variables for aarch64-unknown-linux-gnu target
- Add PKG_CONFIG_PATH and PKG_CONFIG_ALLOW_CROSS for proper library discovery

This resolves the "Could not find directory of OpenSSL installation" error
during ARM64 cross-compilation in GitHub Actions.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>