test(e2e): golden-master Playwright net for the Platform refactor

Locks the five flows the refactor must not break (feed, channel, player,
settings, nav) so later sprints can prove they changed nothing. Adds a thin
data-testid layer and a dedicated seeded non-demo account; the suite runs on
the baked :8080 stack (authoritative) or :5173. No product-behaviour change.

frontend/e2e/tsconfig.json

@@ -0,0 +1,15 @@
+{
+  "compilerOptions": {
+    "target": "ES2022",
+    "module": "ESNext",
+    "moduleResolution": "bundler",
+    "lib": ["ES2022", "DOM", "DOM.Iterable"],
+    "types": ["node", "@playwright/test"],
+    "strict": true,
+    "skipLibCheck": true,
+    "noEmit": true,
+    "esModuleInterop": true,
+    "resolveJsonModule": true
+  },
+  "include": [".", "../playwright.config.ts"]
+}