fix: code review — XSS, type safety, validation improvements

Critical:
- InvoiceDetail: sanitize notes HTML with DOMPurify
- OrderDetail: use proper DOMPurify import instead of window fallback

Important:
- AttendanceBalances: add fund_to_date to interface, remove as-any casts
- All schemas: replace z.any() with z.preprocess for boolean fields
- Routes: simplify boolean coercion (Zod handles it now)

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

src/admin/pages/InvoiceDetail.tsx

@@ -5,6 +5,7 @@ import {
   useParams,
   Link,
 } from "react-router-dom";
+import DOMPurify from "dompurify";
 import { useAlert } from "../context/AlertContext";
 import { useAuth } from "../context/AuthContext";
 import Forbidden from "../components/Forbidden";
@@ -1969,7 +1970,9 @@ export default function InvoiceDetail() {
         <h3 className="admin-card-title">Veřejné poznámky na faktuře</h3>
         {isPaid ? (
           notes && notes.trim() && notes !== "<p><br></p>" ? (
-            <div dangerouslySetInnerHTML={{ __html: notes }} />
+            <div
+              dangerouslySetInnerHTML={{ __html: DOMPurify.sanitize(notes) }}
+            />
           ) : (
             <p className="text-tertiary">Žádné poznámky.</p>
           )