feat: add AI-powered visual regression testing infrastructure

- Add docker-compose.web-testing.yml with vlmkit service
- Add 5 test scripts: capture, compare, pipeline, console-monitor, link-checker
- Add vrt.config.json with 3 viewports + maskSelectors
- Add package.json with @mizchi/vlmkit and Node >=24
- Add tests/README.md with VRT documentation
- Update .gitignore for test artifacts

Based on APAW issue #144 / milestone #106

tests/scripts/capture-screenshots.js

@@ -0,0 +1,84 @@
+const { chromium } = require('playwright');
+const path = require('path');
+const fs = require('fs');
+
+const VIEWPORTS = {
+  mobile: { width: 375, height: 667 },
+  tablet: { width: 768, height: 1024 },
+  desktop: { width: 1280, height: 720 },
+};
+
+function slugify(pagePath) {
+  return pagePath.replace(/^\//, '').replace(/[^a-zA-Z0-9_-]/g, '_') || 'home';
+}
+
+async function capturePage(page, pagePath, viewportName, outputDir) {
+  const fullUrl = `${process.env.TARGET_URL}${pagePath}`;
+  const filename = `${slugify(pagePath)}_${viewportName}.png`;
+  const filepath = path.join(outputDir, filename);
+
+  await page.setViewportSize(VIEWPORTS[viewportName]);
+  await page.goto(fullUrl, { waitUntil: 'networkidle', timeout: 30000 });
+  await page.waitForTimeout(500);
+  await page.screenshot({ path: filepath, fullPage: false });
+
+  return { pagePath, viewport: viewportName, file: filename, saved: true };
+}
+
+async function main() {
+  const mode = process.argv[2];
+  if (!['baseline', 'current'].includes(mode)) {
+    console.error('Usage: node capture-screenshots.js <baseline|current>');
+    process.exit(1);
+  }
+
+  const targetUrl = process.env.TARGET_URL;
+  const pages = (process.env.PAGES || '/').split(',').map(p => p.trim()).filter(p => /^\/[A-Za-z0-9._\/-]*$/.test(p));
+  if (pages.length === 0) {
+    console.error('No valid pages in PAGES environment variable');
+    process.exit(1);
+  }
+  const outputDir = mode === 'baseline'
+    ? (process.env.BASELINE_DIR || './screenshots/baseline')
+    : (process.env.CURRENT_DIR || './screenshots/current');
+
+  if (!targetUrl) {
+    console.error('TARGET_URL environment variable is required');
+    process.exit(1);
+  }
+
+  fs.mkdirSync(outputDir, { recursive: true });
+
+  const browser = await chromium.launch({ headless: true });
+  const context = await browser.newContext();
+  const page = await context.newPage();
+  const results = [];
+
+  try {
+    for (const pagePath of pages) {
+      for (const vpName of Object.keys(VIEWPORTS)) {
+        try {
+          const result = await capturePage(page, pagePath, vpName, outputDir);
+          results.push(result);
+          console.log(`Captured ${pagePath} @ ${vpName} -> ${result.file}`);
+        } catch (err) {
+          results.push({ pagePath, viewport: vpName, error: err.message, saved: false });
+          console.error(`Failed ${pagePath} @ ${vpName}: ${err.message}`);
+        }
+      }
+    }
+  } finally {
+    await browser.close();
+  }
+
+  const report = { mode, targetUrl, pages, outputDir, results };
+  const reportPath = path.join(outputDir, '..', `${mode}-capture-report.json`);
+  fs.mkdirSync(path.dirname(reportPath), { recursive: true });
+  fs.writeFileSync(reportPath, JSON.stringify(report, null, 2));
+  console.log(`Report saved to ${reportPath}`);
+}
+
+main().catch(err => {
+  console.error('Fatal error:', err);
+  process.exit(1);
+});