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/utils/html-to-pdf.ts

@@ -0,0 +1,52 @@
+import { Browser } from "puppeteer";
+
+let browser: Browser | null = null;
+
+async function getBrowser(): Promise<Browser> {
+  if (browser && browser.connected) return browser;
+
+  // Try puppeteer (bundles Chromium), fall back to puppeteer-core (system Chromium)
+  try {
+    const puppeteer = await import("puppeteer");
+    browser = await puppeteer.default.launch({
+      headless: true,
+      args: ["--no-sandbox", "--disable-setuid-sandbox", "--disable-gpu"],
+    });
+  } catch {
+    const core = await import("puppeteer-core");
+    const executablePath =
+      process.env.CHROMIUM_PATH ||
+      "/usr/bin/chromium-browser" ||
+      "/usr/bin/chromium";
+    browser = await core.default.launch({
+      headless: true,
+      executablePath,
+      args: ["--no-sandbox", "--disable-setuid-sandbox", "--disable-gpu"],
+    });
+  }
+
+  return browser;
+}
+
+export async function htmlToPdf(html: string): Promise<Buffer> {
+  const b = await getBrowser();
+  const page = await b.newPage();
+  try {
+    await page.setContent(html, { waitUntil: "networkidle0" });
+    const pdf = await page.pdf({
+      format: "A4",
+      printBackground: true,
+      margin: { top: "10mm", bottom: "10mm", left: "10mm", right: "10mm" },
+    });
+    return Buffer.from(pdf);
+  } finally {
+    await page.close();
+  }
+}
+
+export async function closeBrowser(): Promise<void> {
+  if (browser) {
+    await browser.close();
+    browser = null;
+  }
+}