docs: add AGENTS.md with Cursor Cloud specific setup instructions (#273)

<!-- CURSOR_AGENT_PR_BODY_BEGIN -->
Adds `AGENTS.md` documenting Cursor Cloud dev-environment setup for this
Docusaurus site. No production code changes. Validated: `yarn typecheck`
passes; `yarn start`/`yarn build` available.
<!-- CURSOR_AGENT_PR_BODY_END -->

<div><a
href="https://cursor.com/agents/bc-0d2d55e2-cb0f-49b0-8d5f-15c80c2982c8"><picture><source
media="(prefers-color-scheme: dark)"
srcset="https://cursor.com/assets/images/open-in-web-dark.png"><source
media="(prefers-color-scheme: light)"
srcset="https://cursor.com/assets/images/open-in-web-light.png"><img
alt="Open in Web" width="114" height="28"
src="https://cursor.com/assets/images/open-in-web-dark.png"></picture></a>&nbsp;<a
href="https://cursor.com/background-agent?bcId=bc-0d2d55e2-cb0f-49b0-8d5f-15c80c2982c8"><picture><source
media="(prefers-color-scheme: dark)"
srcset="https://cursor.com/assets/images/open-in-cursor-dark.png"><source
media="(prefers-color-scheme: light)"
srcset="https://cursor.com/assets/images/open-in-cursor-light.png"><img
alt="Open in Cursor" width="131" height="28"
src="https://cursor.com/assets/images/open-in-cursor-dark.png"></picture></a>&nbsp;</div>

Co-authored-by: Cursor Agent <cursoragent@cursor.com>
Co-authored-by: Piotr Wodecki <PiotrWodecki@users.noreply.github.com>

Author: PiotrWodecki

AGENTS.md

@@ -0,0 +1,10 @@
+# documentation
+
+Fishjam documentation site (Docusaurus, Yarn Berry).
+
+## Cursor Cloud specific instructions
+
+Node (via nvm) and Corepack/Yarn are pre-installed; the startup script runs `yarn install`. Non-obvious notes:
+
+- Validated command: `yarn typecheck` (passes).
+- `yarn start` runs the Docusaurus dev server; `yarn build` produces the static site. `yarn generate:python:docs` / `update-api` pull docs from the SDKs and may need those repos/network.