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/users.service.ts

@@ -97,12 +97,10 @@ export async function createUser(data: CreateUserData) {
   const firstName = data.first_name.trim();
   const lastName = data.last_name.trim();
 
-  // Email format
   if (!/^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(email)) {
     return { error: "Neplatný formát e-mailu", status: 400 } as const;
   }
 
-  // Username uniqueness
   const existingUsername = await prisma.users.findFirst({
     where: { username },
   });
@@ -110,7 +108,6 @@ export async function createUser(data: CreateUserData) {
     return { error: "Uživatelské jméno již existuje", status: 409 } as const;
   }
 
-  // Email uniqueness
   const existingEmail = await prisma.users.findFirst({ where: { email } });
   if (existingEmail) {
     return { error: "E-mail již existuje", status: 409 } as const;
@@ -144,7 +141,6 @@ export async function updateUser(id: number, body: UpdateUserData) {
 
   const data: Record<string, unknown> = {};
 
-  // Username validation and uniqueness
   if (body.username !== undefined) {
     const newUsername = String(body.username).trim();
     if (newUsername !== existing.username) {
@@ -161,7 +157,6 @@ export async function updateUser(id: number, body: UpdateUserData) {
     data.username = newUsername;
   }
 
-  // Email validation and uniqueness
   if (body.email !== undefined) {
     const newEmail = String(body.email).trim();
     if (!/^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(newEmail)) {