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/schemas/invoices.schema.ts

@@ -41,7 +41,10 @@ export const CreateInvoiceSchema = z.object({
     .transform((v) => Number(v))
     .optional()
     .default(21.0),
-  apply_vat: z.preprocess(v => v === true || v === 1 || v === "1", z.boolean()).optional().default(true),
+  apply_vat: z
+    .preprocess((v) => v === true || v === 1 || v === "1", z.boolean())
+    .optional()
+    .default(true),
   payment_method: z.string().nullish(),
   constant_symbol: z.string().nullish(),
   bank_name: z.string().nullish(),
@@ -53,6 +56,7 @@ export const CreateInvoiceSchema = z.object({
   tax_date: z.string().nullish(),
   issued_by: z.string().nullish(),
   billing_text: z.string().nullish(),
+  language: z.string().optional().default("cs"),
   notes: z.string().nullish(),
   internal_notes: z.string().nullish(),
   items: z.array(InvoiceItemSchema).optional(),
@@ -61,6 +65,7 @@ export const CreateInvoiceSchema = z.object({
 export const UpdateInvoiceSchema = z.object({
   status: z.string().optional(),
   currency: z.string().optional(),
+  language: z.string().optional(),
   payment_method: z.string().nullish(),
   constant_symbol: z.string().nullish(),
   bank_name: z.string().nullish(),
@@ -73,7 +78,9 @@ export const UpdateInvoiceSchema = z.object({
     .union([z.number(), z.string()])
     .transform((v) => Number(v))
     .optional(),
-  apply_vat: z.preprocess(v => v === true || v === 1 || v === "1", z.boolean()).optional(),
+  apply_vat: z
+    .preprocess((v) => v === true || v === 1 || v === "1", z.boolean())
+    .optional(),
   issue_date: z.union([z.string(), z.null()]).optional(),
   due_date: z.union([z.string(), z.null()]).optional(),
   tax_date: z.union([z.string(), z.null()]).optional(),