fix(dates): use local 'today' for date-input defaults instead of the UTC date

11 form defaults across 6 files used new Date().toISOString().split('T')[0] (the UTC date), which lands on yesterday during the post-midnight Prague window (UTC+1/+2). Added todayLocalStr() (local YYYY-MM-DD) in formatters and replaced them. Future-date expressions (e.g. invoice due_date +14d) left untouched.

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

src/admin/pages/OfferDetail.tsx

@@ -56,7 +56,7 @@ import AdminDatePicker from "../components/AdminDatePicker";
 import RichEditor from "../components/RichEditor";
 import useDebounce from "../hooks/useDebounce";
 import apiFetch from "../utils/api";
-import { formatCurrency } from "../utils/formatters";
+import { formatCurrency, todayLocalStr } from "../utils/formatters";
 import {
   companySettingsOptions,
   type CompanySettingsData,
@@ -101,7 +101,7 @@ const emptyForm: OfferForm = {
   project_code: "",
   customer_id: null,
   customer_name: "",
-  created_at: new Date().toISOString().split("T")[0],
+  created_at: todayLocalStr(),
   valid_until: "",
   currency: "CZK",
   language: "EN",