CLI/API: add a config-driven generate command

[sussdorff]

• Add the advertised generate command, which was documented in the CLI header but did not exist.
• Drive one or more APIBuilder pipelines from a JSON config instead of a hand-written script.
• Resolve relative paths against the config file directory, reject unknown keys, and keep going after a failed builder so every failure is reported in one pass.
• Walk up from the calling module to find generator assets, so the bundled CLI at dist/cli/index.js can load profile-helpers.ts.
• Report --version from package.json instead of a hardcoded 0.1.0.

The CLI currently only emits TypeSchema NDJSON:

atomic-codegen typeschema generate hl7.fhir.r4.core@4.0.1 -o schemas.ndjson

After this change, code generation is a config file:

atomic-codegen generate --config ./codegen.json
atomic-codegen generate --config ./codegen.json --dry-run

{
  "version": 1,
  "builders": [
    {
      "name": "core",
      "fromPackages": [{ "name": "hl7.fhir.r4.core", "version": "4.0.1" }],
      "typescript": {},
      "outputTo": "./out/core",
      "cleanOutput": true
    }
  ]
}