refactor(#240): remove needsExpert feature completely

Drops the needsExpert / needs_expert flag end-to-end: DB migration
(V37, never applied), Document entity field, PATCH endpoint, service
method, DTO field, all three queue queries, ExpertBadge component,
i18n key, generated API types, and test fixture.

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

frontend/src/lib/generated/api.ts

@@ -1225,7 +1225,6 @@ export interface components {
             metadataComplete: boolean;
             /** @enum {string} */
             scriptType: "UNKNOWN" | "TYPEWRITER" | "HANDWRITING_LATIN" | "HANDWRITING_KURRENT";
-            needsExpert: boolean;
             receivers?: components["schemas"]["Person"][];
             sender?: components["schemas"]["Person"];
             tags?: components["schemas"]["Tag"][];
@@ -1489,7 +1488,6 @@ export interface components {
             title: string;
             /** Format: date */
             documentDate?: string;
-            needsExpert: boolean;
             /** Format: int32 */
             annotationCount: number;
             /** Format: int32 */