feat: native YAML import and export

[pskillen]

Problem

We have no native, fully-supported interchange format for our internal data models. Vendor CSV formats are lossy and version-specific.

Intended outcome

Export and import our data in our own native YAML format that fully represents the internal models.

Success criteria: a user can export a CPS from one browser as YAML, import it into another browser, and the internal state across both browsers is identical (within the context of CPS data).

Affected tool(s)

• Shared import/export code consumed by tools/.

Notes

• Stay static (HTML + sidecar JS).
• Depends on the internal data models (genericise-import); complements vendor CPS export.