docs(platform): update AGENTS instructions (#10016)

## Summary
- refine contribution instructions in `autogpt_platform/AGENTS.md`

## Testing
- `pre-commit` *(fails to fetch hooks due to no network access)*

#### For code changes:
- [x] I have clearly listed my changes in the PR description
- [x] I have made a test plan
- [x] I have tested my changes according to the test plan:
  <!-- Put your test plan here: -->
  - [x] Docs only hcnage

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

AGENTS.md

@@ -0,0 +1,50 @@
+# AutoGPT Platform Contribution Guide
+
+This guide provides context for Codex when updating the **autogpt_platform** folder.
+
+## Directory overview
+- `autogpt_platform/backend` – FastAPI based backend service.
+- `autogpt_platform/autogpt_libs` – Shared Python libraries.
+- `autogpt_platform/frontend` – Next.js + Typescript frontend.
+- `autogpt_platform/docker-compose.yml` – development stack.
+
+See `docs/content/platform/getting-started.md` for setup instructions.
+
+## Code style
+- Format Python code with `poetry run format`.
+- Format frontend code using `yarn format`.
+
+## Testing
+- Backend: `poetry run test` (runs pytest with a docker based postgres + prisma).
+- Frontend: `yarn test` or `yarn test-ui` for Playwright tests. See `docs/content/platform/contributing/tests.md` for tips.
+
+Always run the relevant linters and tests before committing.
+Use conventional commit messages for all commits (e.g. `feat(backend): add API`).
+  Types:
+    - feat
+    - fix
+    - refactor
+    - ci
+    - dx (developer experience)
+  Scopes:
+    - platform
+      - platform/library
+      - platform/marketplace
+      - backend
+        - backend/executor
+      - frontend
+        - frontend/library
+        - frontend/marketplace
+      - blocks
+
+## Pull requests
+- Use the template in `.github/PULL_REQUEST_TEMPLATE.md`.
+- Rely on the pre-commit checks for linting and formatting
+- Fill out the **Changes** section and the checklist.
+- Use conventional commit titles with a scope (e.g. `feat(frontend): add feature`).
+- Keep out-of-scope changes under 20% of the PR.
+- Ensure PR descriptions are complete.
+- For changes touching `data/*.py`, validate user ID checks or explain why not needed.
+- If adding protected frontend routes, update `frontend/lib/supabase/middleware.ts`.
+- Use the linear ticket branch structure if given codex/open-1668-resume-dropped-runs
+