feat: add GET/PUT clients endpoints to SettingsController

GET  /api/settings/clients       — list all Betriebe ordered by name
PUT  /api/settings/clients/:id   — update AgrarmonitorBetriebId

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

paperless-backend/src/settings/settings.controller.ts

@@ -385,4 +385,17 @@ export class SettingsController {
 
     return this.corrSettingRepo.save(setting);
   }
+
+  // === Betriebe ===
+  @Get('clients')
+  async getClients() {
+    return this.clientRepo.find({ order: { Name: 'ASC' } });
+  }
+
+  @Put('clients/:id')
+  async updateClient(@Param('id') id: string, @Body() body: { AgrarmonitorBetriebId: number | null }) {
+    const clientId = parseInt(id, 10);
+    await this.clientRepo.update(clientId, { AgrarmonitorBetriebId: body.AgrarmonitorBetriebId ?? null });
+    return this.clientRepo.findOneByOrFail({ Id: clientId });
+  }
 }