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/provider.dto.ts

@@ -0,0 +1,17 @@
+export interface TestConnectionDto {
+  /** Provider identifier to test (e.g. 'ollama', custom provider id) */
+  providerId: string;
+  /** Optional base URL override for ad-hoc testing */
+  baseUrl?: string;
+}
+
+export interface TestConnectionResultDto {
+  providerId: string;
+  reachable: boolean;
+  /** Round-trip latency in milliseconds (present when reachable) */
+  latencyMs?: number;
+  /** Human-readable error when unreachable */
+  error?: string;
+  /** Model ids discovered at the remote endpoint (present when reachable) */
+  discoveredModels?: string[];
+}