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>

lib/reports/__tests__/sie-export.test.ts

@@ -91,7 +91,7 @@ describe('generateSIEExport', () => {
 
     const output = await generateSIEExport('user-1', {
       ...baseOptions,
-      org_number: undefined,
+      org_number: null,
     })
 
     expect(output).not.toContain('#ORGNR')