Add GitHub Actions CI, wire ESLint, lock in Caddy

CI pipeline with parallel jobs for fast feedback:
- typecheck, lint, unit tests, build run in parallel
- e2e tests run after build
- Playwright artifacts uploaded on failure

ESLint wired into both apps with sensible defaults:
- underscore-prefixed unused vars allowed
- root package.json marked as type: module

Architecture updated: Caddy as reverse proxy with auto HTTPS.

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

eslint.config.js

@@ -6,5 +6,13 @@ export default tseslint.config(
   { ignores: ["**/build/", "**/dist/", "**/.react-router/", "**/node_modules/"] },
   js.configs.recommended,
   ...tseslint.configs.recommended,
+  {
+    rules: {
+      "@typescript-eslint/no-unused-vars": [
+        "error",
+        { argsIgnorePattern: "^_", varsIgnorePattern: "^_" },
+      ],
+    },
+  },
   prettier,
 );