feat(dkai): preinstall dev language toolchains

[surrealwolf]

Summary

• Add preinstalled dev toolchains to dkai-dev, dkai-arch, dkai-agent, and dkai-hermes startup scripts: Node.js, pnpm, Python (pip/venv), uv, Go, Rust, Java (OpenJDK, Maven, Gradle), Ruby, PHP, .NET SDK, and C/C++ (gcc/build-essential).
• kubernetes template is unchanged (code-server only; languages via custom image or dotfiles).
• Installation uses distro package managers: apt on DKAI DevPod (Ubuntu), pacman on Arch-based templates; dkai-dev also uses NodeSource, Microsoft .NET feed, and Astral uv install script where needed.
• Document toolchains in docs/build-parameters.md (#preinstalled-dev-toolchains) and update template READMEs.
• Extend === Startup summary === in workspace logs to report detected versions for each toolchain.

Test plan

• make test (terraform init/validate, fmt-check, dkai startup bash -n) passes locally
• Push templates to Coder (coder templates push … --directory templates/<id> --activate=false) for dkai-dev and one Arch template
• Promote version and update a test workspace; confirm startup completes and coder logs shows the expanded startup summary with toolchain versions

Made with Cursor

[cursor]

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