Wire orchestration in src/install.ts (#25)

- install() now composes the v0.1 install path: parseInputs → restoreCache (if enabled) → on miss download + extract + saveCache → buildApiStartupFile → smoke → outputs and GMAT_ROOT env export. The "not implemented" stub is removed.
- BuildApiStartupFile.py and the smoke step run on every invocation (cache hit included), since api_startup_file.txt embeds absolute paths that can shift across runner generations and the smoke is the per-run "install is usable here" contract.
- Each phase is wrapped in core.group for a navigable workflow log; dist/index.js regenerated.

Closes #10

Author: djankov