feat: NAS storage for invoices/offers, code cleanup, date/time fixes

- NAS storage for created invoices (PDF via puppeteer), received invoices,
  and offers with auto-save on create/edit
- Deterministic file paths derived from DB fields (no file_path column needed)
- Separate NAS mount points: NAS_FINANCIALS_PATH, NAS_OFFERS_PATH
- Invoice language field (cs/en) stored per invoice, replaces lang modal
- Invoices list filtered by month/year matching KPI card selection
- Centralized date helpers (src/utils/date.ts) replacing all .toISOString()
  calls that returned UTC instead of local time
- Attendance project switching uses exact time (not rounded)
- Comment cleanup: removed ~100 unnecessary/Czech comments
- Removed as-any casts in orders and attendance
- Prisma migrations: add invoice language, drop received_invoices BLOB columns

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

src/admin/pages/AttendanceHistory.tsx

@@ -156,7 +156,6 @@ export default function AttendanceHistory() {
     fetchData();
   }, [fetchData]);
 
-  // Compute totals client-side from raw records
   const computed = useMemo(() => {
     const [yearStr, monthStr] = month.split("-");
     const monthIndex = parseInt(monthStr, 10) - 1;
@@ -181,11 +180,9 @@ export default function AttendanceHistory() {
       }
     }
 
-    // Compute monthly fund (working days * 8h)
     // Exclude holidays from business days (matching PHP CzechHolidays logic)
     const yr = parseInt(yearStr, 10);
     const mo = parseInt(monthStr, 10) - 1;
-    // Count holiday records to subtract from business days
     const holidayDays = records.filter(
       (r) => (r.leave_type || "work") === "holiday",
     ).length;