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/services/orders.service.ts

@@ -11,9 +11,9 @@ interface OrderItemInput {
   position?: number;
 }
 interface OrderSectionInput {
-  title?: string;
-  title_cz?: string;
-  content?: string;
+  title?: string | null;
+  title_cz?: string | null;
+  content?: string | null;
   position?: number;
 }
 
@@ -331,6 +331,7 @@ export async function createOrder(body: CreateOrderData) {
 
 interface UpdateOrderData {
   [key: string]: unknown;
+  customer_id?: number | string | null;
   items?: OrderItemInput[];
   sections?: OrderSectionInput[];
 }
@@ -342,7 +343,6 @@ export async function updateOrder(id: number, body: UpdateOrderData) {
 
   const currentStatus = existing.status as string;
 
-  // Validate status transition
   if (body.status !== undefined && String(body.status) !== currentStatus) {
     const newStatus = String(body.status);
     const allowed = VALID_TRANSITIONS[currentStatus] || [];