14 add mock data to the data model docs

[anettkva]

Summary

Adds example data that shows how the data model is structured, and documents how AI was used to create it.

This PR also rewrites the root README for the first delivery. That was not part of the issue, but it is included here so the README can link to the example data.

Changes

Example data (docs/examples/)

• 8 JSON files, one per entity in the data model: all 4 apparatus and all 22 element groups, plus a small set of elements, vaults, a variant group, a coach, gymnasts and routines
• The elements, vaults, coach, gymnasts and routines are invented, and the data is for documentation only
• A README in the folder explaining this
• Link to the folder from docs/DATA_MODEL.md

AI usage (docs/AI_USAGE.md)

• New section for the example data, including the prompt that was used

Root README (not planned in the issue)

• Introduction, status, what to review, the dataset, planned functionality, technology and getting started
• The "Working in this repository" section is unchanged

Known issue

not fixed here (discovered when writing 'getting started' readme)

pnpm test and pnpm build fail until pnpm-lock.yaml is updated, because Vitest was added with npm. We need to agree on pnpm or npm first.

Closes #14

[ronjalh]

lgtm