fix(client): parse nested error object in API responses

Server returns `{ error: { message, code } }` but client expected
`{ error: string, code }`, causing "[object Object]" to display
on login failure.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

3 files changed, 11 insertions, 6 deletions

diff --git a/src/client/api/client.test.ts b/src/client/api/client.test.ts
index 16deb28..5489547 100644
--- a/src/client/api/client.test.ts
+++ b/src/client/api/client.test.ts
@@ -85,8 +85,10 @@ describe("ApiClient", () => {
 				{
 					status: 401,
 					body: {
-						error: "Invalid username or password",
-						code: "INVALID_CREDENTIALS",
+						error: {
+							message: "Invalid username or password",
+							code: "INVALID_CREDENTIALS",
+						},
 					},
 				},
 			]);
diff --git a/src/client/api/client.ts b/src/client/api/client.ts
index 36a7431..7741942 100644
--- a/src/client/api/client.ts
+++ b/src/client/api/client.ts
@@ -66,9 +66,10 @@ export class ApiClient {
 		if (!response.ok) {
 			const errorBody = (await response.json().catch(() => ({}))) as ApiError;
 			throw new ApiClientError(
-				errorBody.error || `Request failed with status ${response.status}`,
+				errorBody.error?.message ||
+					`Request failed with status ${response.status}`,
 				response.status,
-				errorBody.code,
+				errorBody.error?.code,
 			);
 		}
 
diff --git a/src/client/api/types.ts b/src/client/api/types.ts
index d5df182..eaf69eb 100644
--- a/src/client/api/types.ts
+++ b/src/client/api/types.ts
@@ -10,8 +10,10 @@ export interface AuthResponse {
 }
 
 export interface ApiError {
-	error: string;
-	code?: string;
+	error: {
+		message: string;
+		code: string;
+	};
 }
 
 export interface Tokens {