Scaffold project foundation

Fresh start: Vite + React 19 + strict TS, Tailwind v4, PWA, Vitest/Playwright.
Replaces the prior DeepSeek-built app (deleted; ~135 documented bugs, no VCS).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tsconfig.json

@@ -0,0 +1,7 @@
+{
+  "files": [],
+  "references": [
+    { "path": "./tsconfig.app.json" },
+    { "path": "./tsconfig.node.json" }
+  ]
+}