Document reproducible contributor checks (#105)

docs/CONTRIBUTING.md

@@ -16,4 +16,18 @@ See [LOCAL_DEVELOPMENT.md](./LOCAL_DEVELOPMENT.md) for how to run the app locall
 
 - Keep PRs focused: one feature or fix per PR.
 - For larger features, open an issue first so we can align on the approach before you invest time.
-- Make sure `pnpm ci:check` passes before requesting review.
+- Before requesting review, run the same root checks used by CI:
+
+  ```sh
+  pnpm ci:check
+  pnpm test:ci
+  pnpm vite build
+  ```
+
+- If you changed the website under `web/`, also run:
+
+  ```sh
+  pnpm --dir web install --frozen-lockfile
+  pnpm --dir web run types:check
+  pnpm --dir web run build
+  ```

docs/LOCAL_DEVELOPMENT.md

@@ -3,18 +3,24 @@
 ## Prerequisites
 
 - Node.js 20+
-- [pnpm](https://pnpm.io/)
+- [Corepack](https://nodejs.org/api/corepack.html) (bundled through Node.js 24; install it separately on Node.js 25+)
 - A DataForSEO account/API credentials
 
 ## Local Development Workflow
 
 ```sh
-pnpm install
+# Activates the exact pnpm version declared in package.json.
+corepack enable
+pnpm install --frozen-lockfile
 
 # Run once per fresh local DB
 pnpm run db:migrate:local
 ```
 
+Verify that `pnpm --version` reports the version declared by the
+`packageManager` field in `package.json`. An older global pnpm may reject
+the repository's lockfile as incompatible.
+
 Configure `.env.local`:
 
 1. `cp .env.example .env.local`