Add Next.js frontend PWA

- Pages: login, register, tasks list, task detail
- Components: TaskCard, TaskForm, GroupSelector, StatusBadge, Header
- Tailwind CSS, dark/light mode, PWA manifest
- Running on :3001 via systemd

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

apps/tasks/.eslintrc.json

@@ -0,0 +1,6 @@
+{
+  "extends": "next/core-web-vitals",
+  "rules": {
+    "@typescript-eslint/no-explicit-any": "off"
+  }
+}