feat(1099): add authenticated blob downloads to report API service

Add downloadCsv/downloadCopyB returning Blob via HttpClient so the auth
interceptor attaches the bearer token (raw window.open would 401). Remove
the now-unused copyBUrl/exportCsvUrl raw-URL builders.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

APP/src/app/features/payee1099/services/form1099-report-api.service.ts

@@ -30,11 +30,19 @@ export class Form1099ReportApiService {
     });
   }
 
-  copyBUrl(payeeId: number, taxYear: number): string {
-    return `${this.endpoint}/recipient/${payeeId}/copy-b?taxYear=${taxYear}`;
+  // Authenticated blob downloads: routed through HttpClient so the auth
+  // interceptor attaches the bearer token (a raw window.open would 401).
+  downloadCsv(taxYear: number): Observable<Blob> {
+    return this.http.get(`${this.endpoint}/export-csv`, {
+      params: { taxYear: String(taxYear) },
+      responseType: 'blob',
+    });
   }
 
-  exportCsvUrl(taxYear: number): string {
-    return `${this.endpoint}/export-csv?taxYear=${taxYear}`;
+  downloadCopyB(payeeId: number, taxYear: number): Observable<Blob> {
+    return this.http.get(`${this.endpoint}/recipient/${payeeId}/copy-b`, {
+      params: { taxYear: String(taxYear) },
+      responseType: 'blob',
+    });
   }
 }