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>

prisma/migrations/20260326_add_invoice_language/migration.sql

@@ -0,0 +1 @@
+ALTER TABLE `invoices` ADD COLUMN `language` VARCHAR(5) DEFAULT 'cs' AFTER `billing_text`;

prisma/migrations/20260326_add_received_invoice_file_path/migration.sql

@@ -0,0 +1,2 @@
+-- Add file_path column for NAS storage of received invoice files
+ALTER TABLE `received_invoices` ADD COLUMN `file_path` VARCHAR(500) NULL AFTER `file_data`;

prisma/migrations/20260326_drop_received_invoice_blob_columns/migration.sql

@@ -0,0 +1,4 @@
+-- Remove file_data (BLOB) and file_path columns — files are now stored on NAS
+-- Path is derived from year, month, and file_name
+ALTER TABLE `received_invoices` DROP COLUMN `file_data`;
+ALTER TABLE `received_invoices` DROP COLUMN `file_path`;

prisma/migrations/migration_lock.toml

@@ -0,0 +1,3 @@
+# Please do not edit this file manually
+# It should be added in your version-control system (i.e. Git)
+provider = "mysql"