Docs: write a short "export your data" how-to

[ali-maher-m]

What

RyTask already ships a full workspace + CSV export. Write a short how-to that shows users how to export their data and what the CSV columns mean.

Where

• New page under apps/docs/content/docs/. The export code is in apps/api/src/modules/export/ (see domain/export-csv.ts for the actual columns).

How to verify

Run the docs site; cross-check the documented columns against export-csv.ts so they match exactly.

Notes

Great first issue if you prefer writing to coding.