fix(ci): configure Puppeteer to use system Chromium

Set PUPPETEER_EXECUTABLE_PATH to point to apt-installed chromium.
This allows PDF tests to run without downloading Chrome separately.

Author: alpha912

.github/workflows/ci.yml

@@ -57,6 +57,10 @@ jobs:
           sudo apt-get update
           sudo apt-get install -y chromium-browser
         
+      - name: Configure Puppeteer
+        if: runner.os == 'Linux'
+        run: echo "PUPPETEER_EXECUTABLE_PATH=/usr/bin/chromium-browser" >> $GITHUB_ENV
+        
       - name: Type check
         run: pnpm run typecheck
 
@@ -226,6 +230,10 @@ jobs:
           sudo apt-get update
           sudo apt-get install -y chromium-browser
         
+      - name: Configure Puppeteer
+        if: runner.os == 'Linux'
+        run: echo "PUPPETEER_EXECUTABLE_PATH=/usr/bin/chromium-browser" >> $GITHUB_ENV
+        
       - name: Build packages
         run: pnpm run build