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/ExtensionWorkspaceLoader.tsx

@@ -24,8 +24,8 @@ export default function ExtensionWorkspaceLoader({
         <WorkspaceComponent userId={userId} />
       ) : (
         <EmptyExtensionState
-          title="Kommer snart"
-          description={`${definition.name} \u00e4r under utveckling och kommer snart att vara tillg\u00e4ngligt.`}
+          title="Bakgrundstjänst"
+          description={`${definition.name} körs i bakgrunden och har ingen egen vy. Du kan hantera inställningar under Inställningar.`}
         />
       )}
     </ExtensionWorkspaceShell>