fix: Add Chromium to Docker for PDF certificate generation

- Install chromium in Alpine Dockerfile
- Add PUPPETEER_EXECUTABLE_PATH env var support
- Fallback to system Chrome paths if bundled Chrome not found

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/services/ai-kurzy/certificate.service.js

@@ -294,10 +294,48 @@ export const generateCertificate = async (registraciaId, templateName = 'AIcerti
   // Launch Puppeteer and generate PDF
   let browser;
   try {
-    browser = await puppeteer.launch({
+    const launchOptions = {
       headless: true,
-      args: ['--no-sandbox', '--disable-setuid-sandbox'],
-    });
+      args: ['--no-sandbox', '--disable-setuid-sandbox', '--disable-gpu', '--disable-dev-shm-usage'],
+    };
+
+    // Use PUPPETEER_EXECUTABLE_PATH env var if set (for Docker), otherwise try system paths
+    const executablePath = process.env.PUPPETEER_EXECUTABLE_PATH;
+    if (executablePath) {
+      launchOptions.executablePath = executablePath;
+      logger.info(`Using Chrome from PUPPETEER_EXECUTABLE_PATH: ${executablePath}`);
+    }
+
+    try {
+      browser = await puppeteer.launch(launchOptions);
+    } catch (launchError) {
+      // If no env var set, try common system Chrome paths
+      if (!executablePath) {
+        const systemChromePaths = [
+          '/usr/bin/chromium-browser',
+          '/usr/bin/chromium',
+          '/usr/bin/google-chrome',
+          '/usr/bin/google-chrome-stable',
+        ];
+
+        for (const chromePath of systemChromePaths) {
+          try {
+            await fs.access(chromePath);
+            logger.info(`Using system Chrome at: ${chromePath}`);
+            browser = await puppeteer.launch({
+              ...launchOptions,
+              executablePath: chromePath,
+            });
+            break;
+          } catch {
+            // Continue to next path
+          }
+        }
+      }
+      if (!browser) {
+        throw new Error('Chrome nie je nainštalovaný. Pridajte do Dockerfile: RUN apk add --no-cache chromium && ENV PUPPETEER_EXECUTABLE_PATH=/usr/bin/chromium-browser');
+      }
+    }
 
     const page = await browser.newPage();
     await page.setContent(html, { waitUntil: 'networkidle0' });