Harden API, data layer, and autosave; add validation, pagination, migrations

- Enforce task ownership on PATCH/DELETE /api/tasks (was: any signed-in
  user could edit or delete anyone's tasks)
- Validate all API request bodies with zod; escape user content and
  restrict links to http(s) in the Drive export; block reverting a
  SUBMITTED report
- Add @@unique([userId, date]) on Report with upsert to eliminate the
  duplicate-daily-report race; switch startup from
  `prisma db push --accept-data-loss` to `prisma migrate deploy` with
  automatic baselining of existing databases (dedup migration merges
  any pre-existing duplicates)
- Autosave: re-queue and retry failed task saves with a visible
  saving/error indicator instead of silently dropping edits
- Paginate and filter GET /api/reports (?date, ?mine, ?q, ?take,
  ?cursor); report form fetches only today's report, admin dashboard
  uses server-side search + Load more
- Type the frontend and lib layer (DTOs in src/types/api.ts); zero
  eslint errors
- Update README and Unraid guide for migrations, upgrade path, and API

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

package.json

@@ -18,7 +18,8 @@
     "next-auth": "^4.24.13",
     "prisma": "^7.5.0",
     "react": "19.2.3",
-    "react-dom": "19.2.3"
+    "react-dom": "19.2.3",
+    "zod": "^4.4.3"
   },
   "devDependencies": {
     "@tailwindcss/postcss": "^4",