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/Attendance.tsx

@@ -755,10 +755,7 @@ export default function Attendance() {
                               {formatTime(shift.departure_time)}
                             </td>
                             <td className="admin-mono">
-                              {formatMinutes(
-                                calculateWorkMinutes(shift as any),
-                                true,
-                              )}
+                              {formatMinutes(calculateWorkMinutes(shift), true)}
                             </td>
                             {projects.length > 0 && (
                               <td>