refactor: consolidate AI analyzers into shared lib/ai module and add journal entry reversal columns

Extract shared vision/document analysis logic into lib/ai (vision-client, document-analyzer,
image preprocessing, validation helpers), simplifying invoice-analyzer, receipt-analyzer, and
document classifier. Add migration 046 for journal entry reversal/correction link columns
(reversed_by_id, reverses_id, correction_of_id) required by storno service. Update extension
components and shared UI.

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

components/extensions/ExtensionWorkspaceShell.tsx

@@ -20,7 +20,7 @@ export default function ExtensionWorkspaceShell({
       {/* Breadcrumb */}
       <nav className="flex items-center gap-1.5 text-sm text-muted-foreground mb-6">
         <Link href="/extensions" className="hover:text-foreground transition-colors">
-          Till\u00e4gg
+          Tillägg
         </Link>
         <span>/</span>
         <Link