Class ConfigLoader

Creates a ConfigLoader pointing at the given config file path.

Loads, merges, and validates the full importer configuration.

Loads and merges config without running validation — used by --validate mode.

Loads and merges the on-disk config (config.json + credentials.json) WITHOUT applying runtime environment overrides, so an ephemeral variable such as PROXY_SERVER is never folded in and then baked into the file. The portal store — which edits this config and writes it back — uses this so a runtime override can never be silently persisted over the operator's real config.

Boot-gate validation seam: enforces the exact "is this config bootable?" rules the importer applies at startup, without file loading. The portal write-gate calls this so a saved config can never pass the portal yet make the importer exit(1). Delegates to the loader's own private validation, the same check the loader runs after merging files, so the two cannot drift.