feat(web): provider management UI — list, test, model capabilities (#123) (#142)

Co-authored-by: Jason Woltje <jason@diversecanvas.com>
Co-committed-by: Jason Woltje <jason@diversecanvas.com>

apps/gateway/src/agent/providers.controller.ts

@@ -3,6 +3,7 @@ import type { RoutingCriteria } from '@mosaic/types';
 import { AuthGuard } from '../auth/auth.guard.js';
 import { ProviderService } from './provider.service.js';
 import { RoutingService } from './routing.service.js';
+import type { TestConnectionDto, TestConnectionResultDto } from './provider.dto.js';
 
 @Controller('api/providers')
 @UseGuards(AuthGuard)
@@ -22,6 +23,11 @@ export class ProvidersController {
     return this.providerService.listAvailableModels();
   }
 
+  @Post('test')
+  testConnection(@Body() body: TestConnectionDto): Promise<TestConnectionResultDto> {
+    return this.providerService.testConnection(body.providerId, body.baseUrl);
+  }
+
   @Post('route')
   route(@Body() criteria: RoutingCriteria) {
     return this.routingService.route(criteria);