chore(frontend): move from yarn1 to pnpm (#10072)

## 🧢 Overview
This PR migrates the AutoGPT Platform frontend from [yarn
1](https://classic.yarnpkg.com/lang/en/) to [pnpm](https://pnpm.io/)
using **corepack** for automatic package manager management.

**yarn1** is not longer maintained and a bit old, moving to **pnpm** we
get:
- ⚡ Significantly faster install times,
- 💾 Better disk space efficiency,
- 🛠️ Better community support and maintenance,
- 💆🏽‍♂️  Config swap very easy

##  🏗️ Changes

### Package Management Migration

- updated [corepack](https://github.com/nodejs/corepack) to use
[pnpm](https://pnpm.io/)
- Deleted `yarn.lock` and generated new `pnpm-lock.yaml`
- Updated `.gitignore`

### Documentation Updates

- `frontend/README.md`: 
  - added comprehensive tech stack overview with links
  - updated all commands to use pnpm
  - added corepack setup instructions
  - and included migration disclaimer for yarn users
- `backend/README.md`: 
  - Updated installation instructions to use pnpm with corepack
- `AGENTS.md`: 
  - Updated testing commands from yarn to pnpm

### CI/CD & Infrastructure

- **GitHub Workflows** : 
  - updated all jobs to use pnpm with corepack enable
  - cleaned FE Playwright test workflow to avoid Sentry noise
- **Dockerfile**:
- updated to use pnpm with corepack, changed lock file reference, and
updated cache mount path

###  📋 Checklist

#### 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:
  
  **Test Plan:**
  > assuming you are on the `frontend` folder 
- [x] Clean installation works: `rm -rf node_modules && corepack enable
&& pnpm install`
  - [x] Development server starts correctly: `pnpm dev`
  - [x] Build process works: `pnpm build`
  - [x] Linting and formatting work: `pnpm lint` and `pnpm format`
  - [x] Type checking works: `pnpm type-check`
  - [x] Tests run successfully: `pnpm test`
  - [x] Storybook starts correctly: `pnpm storybook`
  - [x] Docker build succeeds with new pnpm configuration
  - [x] GitHub Actions workflow passes with pnpm commands

#### For configuration changes:
- [x] `.env.example` is updated or already compatible with my changes
- [x] `docker-compose.yml` is updated or already compatible with my
changes
- [x] I have included a list of my configuration changes in the PR
description (under **Changes**)

AGENTS.md

@@ -3,6 +3,7 @@
 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.
@@ -11,12 +12,14 @@ This guide provides context for Codex when updating the **autogpt_platform** fol
 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`.
+- Format frontend code using `pnpm 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.
+- Frontend: `pnpm test` or `pnpm 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`).
@@ -38,6 +41,7 @@ Use conventional commit messages for all commits (e.g. `feat(backend): add API`)
       - 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.
@@ -47,4 +51,3 @@ Use conventional commit messages for all commits (e.g. `feat(backend): add API`)
 - 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
-