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/nas-file-manager.ts

@@ -1,6 +1,7 @@
 import fs from "fs";
 import path from "path";
 import { config } from "../config/env";
+import { localDateStr, localTimeStr } from "../utils/date";
 
 const FileType = require("file-type") as typeof import("file-type");
 
@@ -223,16 +224,7 @@ export class NasFileManager {
       }
 
       const modified = lstat.mtime;
-      const modifiedStr =
-        modified.getFullYear() +
-        "-" +
-        String(modified.getMonth() + 1).padStart(2, "0") +
-        "-" +
-        String(modified.getDate()).padStart(2, "0") +
-        " " +
-        String(modified.getHours()).padStart(2, "0") +
-        ":" +
-        String(modified.getMinutes()).padStart(2, "0");
+      const modifiedStr = `${localDateStr(modified)} ${localTimeStr(modified)}`;
 
       const item: FileItem = {
         name: entry,
@@ -284,7 +276,6 @@ export class NasFileManager {
       }
     }
 
-    // Real path on disk for UI display
     let realDirPath: string;
     try {
       realDirPath = fs.realpathSync(dirPath);
@@ -331,7 +322,6 @@ export class NasFileManager {
       return "Tento typ souboru není povolen";
     }
 
-    // MIME validation via file-type
     try {
       const typeResult = await FileType.fromBuffer(fileBuffer);
       if (typeResult && this.isSuspiciousMime(typeResult.mime, ext)) {
@@ -343,7 +333,6 @@ export class NasFileManager {
 
     let destPath = dirPath + "/" + safeName;
 
-    // If file exists, append counter
     if (fs.existsSync(destPath)) {
       const base = path.basename(safeName, ext ? "." + ext : "");
       let counter = 1;
@@ -456,7 +445,6 @@ export class NasFileManager {
       return "Cílový soubor již existuje";
     }
 
-    // Validate target name
     const targetName = path.basename(toPath);
     if (this.sanitizeFilename(targetName) !== targetName) {
       return "Neplatný cílový název";
@@ -513,7 +501,6 @@ export class NasFileManager {
 
   public sanitizeFilename(name: string): string {
     let safe = path.basename(name);
-    // Strip control chars and special chars
     safe = safe.replace(/[\x00-\x1f\x7f<>:"/\\|?*]/g, "");
     safe = safe.replace(/^[. ]+|[. ]+$/g, "");
 
@@ -583,7 +570,6 @@ export class NasFileManager {
       return null;
     }
 
-    // Normalize separators and trim
     const normalized = subPath.replace(/\\/g, "/").replace(/^\/+|\/+$/g, "");
     const candidate = path.resolve(folderPath, normalized).replace(/\\/g, "/");
 
@@ -618,7 +604,6 @@ export class NasFileManager {
     const normalFull = fullPath.replace(/\\/g, "/");
     const normalBase = basePath.replace(/\\/g, "/");
 
-    // Get the relative portion after basePath
     if (!normalFull.startsWith(normalBase)) {
       return false;
     }