test: add end-to-end browser tests with Playwright

Set up tests/e2e/ with a login page test covering branding, accessibility,
form structure, theme colors, and static asset serving. Includes run.sh
that manages the app lifecycle (start, test, stop) automatically.

tests/e2e/package.json

@@ -0,0 +1,12 @@
+{
+  "private": true,
+  "name": "porchlight-e2e",
+  "description": "End-to-end browser tests for Porchlight",
+  "scripts": {
+    "test": "./run.sh",
+    "setup": "npx playwright install chromium"
+  },
+  "dependencies": {
+    "playwright": "^1.52.0"
+  }
+}