feat: trivial one-line installer (install.ps1 / install.sh)
Replace the manual binary download with a one-line installer per OS that addresses the onboarding REX (labdev not on PATH, no install step):
- Downloads the release binary, verifies SHA256 against SHA256SUMS.
- Installs per-user (no admin): %LocalAppData%\Programs\labdev / ~/.local/bin.
- Adds the install dir to the user PATH, idempotently.
- Pre-creates the OS-native settings + cache dirs labdev resolves (os.UserConfigDir / os.UserCacheDir; macOS uses ~/Library, not ~/.config) and drops a commented config.example.yaml placeholder.
- Offers to run
labdev setup; never blocks inirm|iex/curl|sh. - Supports LABDEV_VERSION (pin tag), LABDEV_FORGE_TOKEN (private download), LABDEV_RUN_SETUP.
.gitattributes forces LF on install.sh so the raw-served script keeps a valid shebang. README install section rewritten (one-liner + manual fallback).