feat: transaction categorization UX improvements and description matching

Add journal entry preview, human-readable account names, auto-apply VAT,
fallback template suggestions, example prompts, invoice match comparison,
and batch result feedback. Also includes user-description-match extension,
describe/batch-describe API routes, improved AI categorization with multi-
suggestion support, and template embedding search.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/api/invoices/[id]/send/__tests__/route.test.ts

@@ -72,6 +72,8 @@ describe('POST /api/invoices/[id]/send', () => {
         unit: 'tim',
         unit_price: 1000,
         line_total: 10000,
+        vat_rate: 25,
+        vat_amount: 2500,
         created_at: '2024-06-15T14:30:00Z',
       },
     ],

app/api/invoices/__tests__/route.test.ts

@@ -318,6 +318,8 @@ describe('POST /api/invoices (create credit note)', () => {
         unit: 'tim',
         unit_price: 1000,
         line_total: 10000,
+        vat_rate: 25,
+        vat_amount: 2500,
         created_at: '2024-06-15T14:30:00Z',
       },
     ]
@@ -385,6 +387,8 @@ describe('POST /api/invoices (create credit note)', () => {
           unit: 'st',
           unit_price: 1000,
           line_total: 1000,
+          vat_rate: 25,
+          vat_amount: 250,
           created_at: '2024-06-15T14:30:00Z',
         },
       ],