Auto-install toolchains for language builders

[richardkiene]

Summary

When building projects that require external toolchains (Go/TinyGo, .NET, Rust/cargo-component), automatically download and manage the required toolchains instead of requiring manual installation.

Motivation

Currently, users must manually install language toolchains before using Fabricks to build projects. This adds friction to the onboarding experience.

Proposed Solution

Implement automatic toolchain management similar to rustup:

1. Toolchain detection - Check if required toolchain is installed
2. Auto-download - Download toolchain binaries if missing
3. Version management - Support multiple toolchain versions
4. Cache management - Store toolchains in ~/.fabricks/toolchains/

Toolchains to support

Language	Toolchain	Download source
Go	TinyGo	https://github.com/tinygo-org/tinygo/releases
C#/.NET	.NET SDK	https://dotnet.microsoft.com/download
Rust	cargo-component	Via cargo install

Implementation Notes

• Could use platform-specific binary downloads
• Need to handle PATH setup for subprocess calls
• Consider checksum verification for security
• May want opt-out flag for users who prefer manual management

Related

• Depends on: Add Go and C# .NET language support #31 (Go and .NET support)
• Alternative approach: Evaluate container-based builds for language compilation #33 (container-based builds)