chore(repo): migrate from npm to pnpm workspace

.husky/commit-msg

@@ -1 +1 @@
-npx --no-install commitlint --edit "$1"
+pnpm exec commitlint --edit "$1"

.husky/pre-commit

@@ -1 +1 @@
-npx lint-staged
+pnpm exec lint-staged

CONTRIBUTING.md

@@ -81,14 +81,22 @@ python scripts/seed_problems.py   # load problems from YAML
 python app.py
 ```
 
-One-time, from the repo root, install the Git hook tooling (requires Node 18+):
+One-time, from the repo root, install the JavaScript tooling. This repo uses
+[pnpm](https://pnpm.io/) (a pnpm workspace covers the root tooling and the
+`frontend/` app). Enable it via Corepack, which ships with Node 18+:
 
 ```bash
-npm install   # sets up Husky pre-commit + commit-msg hooks
+corepack enable               # makes the pinned pnpm version available
+pnpm install                  # installs frontend deps + sets up Git hooks
 ```
 
-This activates auto-formatting and commit-message validation on every commit
-(see [Git hooks](#git-hooks) and [Commit messages](#commit-messages) below).
+`pnpm install` also activates auto-formatting and commit-message validation on
+every commit (see [Git hooks](#git-hooks) and [Commit messages](#commit-messages)
+below). The pnpm version is pinned via the `packageManager` field in the root
+`package.json`.
+
+The frontend can then be run from the repo root: `pnpm dev` (or `pnpm build` /
+`pnpm lint`), which proxy to the `frontend` workspace.
 
 ### Running tests
 
@@ -127,7 +135,7 @@ sure both pass locally first.
 
 ### Git hooks
 
-After `npm install` (repo root), [Husky](https://typicode.github.io/husky/)
+After `pnpm install` (repo root), [Husky](https://typicode.github.io/husky/)
 installs two hooks that run automatically:
 
 - **`pre-commit`** — runs [lint-staged](https://github.com/lint-staged/lint-staged)

frontend/README.md

@@ -2,16 +2,16 @@ This is a [Next.js](https://nextjs.org) project bootstrapped with [`create-next-
 
 ## Getting Started
 
-First, run the development server:
+This app is part of a [pnpm workspace](https://pnpm.io/workspaces). Install
+dependencies once from the **repo root** (`pnpm install`), then run the dev
+server either from the root or from this directory:
 
 ```bash
-npm run dev
-# or
-yarn dev
+pnpm dev          # from the repo root (proxies to this workspace)
 # or
+pnpm --filter frontend dev
+# or, from inside frontend/
 pnpm dev
-# or
-bun dev
 ```
 
 Open [http://localhost:3000](http://localhost:3000) with your browser to see the result.