build: migrate from npm to pnpm

- Add packageManager field to package.json for Corepack
- Update GitHub Actions workflow to use pnpm/action-setup
- Update CLAUDE.md commands documentation
- Replace package-lock.json with pnpm-lock.yaml
- Add .npmrc with 7-day minimum-version-age

Author: capytan

.github/workflows/deploy.yml

@@ -20,18 +20,21 @@ jobs:
     steps:
       - name: Checkout
         uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
-      
+
+      - name: Setup pnpm
+        uses: pnpm/action-setup@a7487c7e89a18df4991f7f222e4898a00d66ddda # v4.1.0
+
       - name: Setup Node
         uses: actions/setup-node@49933ea5288caeca8642d1e84afbd3f7d6820020 # v4.4.0
         with:
           node-version: "20"
-          cache: 'npm'
-      
+          cache: 'pnpm'
+
       - name: Install dependencies
-        run: npm ci
-      
+        run: pnpm install --frozen-lockfile
+
       - name: Build
-        run: npm run build
+        run: pnpm run build
 
       - name: Upload artifact
         uses: actions/upload-pages-artifact@56afc609e74202658d3ffba0e8f6dda462b719fa # v3.0.1

.npmrc

@@ -0,0 +1,2 @@
+# 7 days = 60 * 24 * 7 = 10080 minutes
+minimum-version-age=10080

CLAUDE.md

@@ -9,11 +9,11 @@ A Linktree-style personal link collection site built with Next.js. Deployed as a
 ## Commands
 
 ```bash
-npm run dev          # Start development server (http://localhost:3000)
-npm run build        # Build for production (outputs to ./out)
-npm run lint         # Run ESLint
-npm run format       # Format code with Prettier
-npm run format:check # Check formatting without modifying
+pnpm dev          # Start development server (http://localhost:3000)
+pnpm build        # Build for production (outputs to ./out)
+pnpm lint         # Run ESLint
+pnpm format       # Format code with Prettier
+pnpm format:check # Check formatting without modifying
 ```
 
 ## Architecture