v1.6.8: remove offer exchange rate, add invoice item description, offer filters, table animations

- Remove exchange_rate and exchange_rate_date from quotations (schema, service, PDF, form)
- Add item_description field to invoice_items (schema, migration, service, form, PDF)
- Add offer status/customer/order filters with tab-based UI
- Clean up offer statuses to active/ordered/invalidated
- Allow invalidate action for non-ordered offers (not just expired)
- Add fade animations on offers and invoices table data changes

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

prisma/migrations/20260528000000_remove_offer_exchange_rate/migration.sql

@@ -0,0 +1,3 @@
+-- AlterTable
+ALTER TABLE `quotations` DROP COLUMN `exchange_rate`;
+ALTER TABLE `quotations` DROP COLUMN `exchange_rate_date`;

prisma/migrations/20260528000001_add_invoice_item_description/migration.sql

@@ -0,0 +1,2 @@
+-- AlterTable
+ALTER TABLE `invoice_items` ADD COLUMN `item_description` TEXT NULL;