feat: add [[tools.github]] installer type

[nilshamerlinck]

Summary

• Adds a new [[tools.github]] config section for installing tools directly from GitHub releases
• Supports three modes: latest-release auto-resolution, install script, and binary asset download
• Updates the example config (odoo_dev.toml) to use the new format for nvm

Details

Config format:

[[tools.github]]
name = "nvm"
repo = "https://github.com/nvm-sh/nvm"
version = "latest-release"   # or a specific tag like "v0.39.7"
script = "install.sh"        # omit to download a binary asset instead

Behaviour:

1. version = "latest-release" → calls the GitHub Releases API to resolve the current tag before proceeding
2. script defined → constructs https://raw.githubusercontent.com/{owner}/{repo}/{version}/{script} and delegates to the existing _install_script() helper
3. script not defined → fetches release assets via the API, picks the one matching the current OS/arch (handles .tar.gz, .tgz, .zip, plain binaries), installs to ~/.local/bin/{name}

Test plan

• make check passes (linting + type checks)
• make test passes (57 tests)
• Dry-run: tlc install-tools --dry-run shows GitHub tools section
• Live: nvm installs correctly via [[tools.github]] with version = "latest-release" and script = "install.sh"

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