Add Playwright job summary to CI

Generates a markdown summary table in GitHub Actions showing
passed/failed tests with timing per test. Uses the JSON reporter
to output results, then a Node script to format as markdown
and append to $GITHUB_STEP_SUMMARY.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

playwright.config.ts

@@ -6,7 +6,9 @@ export default defineConfig({
   fullyParallel: true,
   retries: process.env.CI ? 2 : 0,
   workers: process.env.CI ? 1 : undefined,
-  reporter: process.env.CI ? [["github"], ["html", { open: "never" }]] : "list",
+  reporter: process.env.CI
+    ? [["github"], ["html", { open: "never" }], ["json", { outputFile: "playwright-results.json" }]]
+    : "list",
   use: {
     baseURL: "http://localhost:3000",
     trace: "on-first-retry",