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/server.ts

@@ -6,7 +6,6 @@ import path from "path";
 import { config } from "./config/env";
 import { securityHeaders } from "./middleware/security";
 
-// Route imports
 import authRoutes from "./routes/admin/auth";
 import usersRoutes from "./routes/admin/users";
 import rolesRoutes from "./routes/admin/roles";
@@ -194,6 +193,8 @@ async function start() {
       await app.close();
       const { default: prisma } = await import("./config/database");
       await prisma.$disconnect();
+      const { closeBrowser } = await import("./utils/html-to-pdf");
+      await closeBrowser();
       app.log.info("Server shut down successfully");
       process.exit(0);
     } catch (err) {