✨ feat: add @manacore/shared-api-client package

Create unified API client for all web apps with:
- createApiClient factory function
- ApiResult<T> Go-style error handling
- HTTP methods: get, post, put, patch, delete, upload
- Auto token handling via getAuthToken callback
- Timeout support with AbortController
- Retry logic with exponential backoff
- Runtime URL injection for Docker
- FormData support for file uploads

Migrate clock app as proof of concept:
- Replace local fetchApi with shared createApiClient
- Update stores to use ApiError.message

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

packages/shared-api-client/src/utils.ts

@@ -0,0 +1,94 @@
+/**
+ * API Client Utilities
+ */
+
+import type { ApiError, ApiErrorCode } from './types';
+
+/**
+ * Build a query string from parameters object
+ * Handles undefined values and proper encoding
+ */
+export function buildQueryString(
+	params: Record<string, string | number | boolean | undefined>
+): string {
+	const searchParams = new URLSearchParams();
+
+	for (const [key, value] of Object.entries(params)) {
+		if (value !== undefined && value !== null && value !== '') {
+			searchParams.append(key, String(value));
+		}
+	}
+
+	const queryString = searchParams.toString();
+	return queryString ? `?${queryString}` : '';
+}
+
+/**
+ * Determine error code from HTTP status
+ */
+export function getErrorCodeFromStatus(status: number): ApiErrorCode {
+	if (status === 401) return 'UNAUTHORIZED';
+	if (status === 403) return 'FORBIDDEN';
+	if (status === 404) return 'NOT_FOUND';
+	if (status === 422 || status === 400) return 'VALIDATION_ERROR';
+	if (status >= 500) return 'SERVER_ERROR';
+	return 'UNKNOWN';
+}
+
+/**
+ * Create a standardized API error
+ */
+export function createApiError(
+	message: string,
+	code: ApiErrorCode,
+	status?: number,
+	details?: unknown
+): ApiError {
+	return { message, code, status, details };
+}
+
+/**
+ * Parse error response body
+ */
+export async function parseErrorResponse(response: Response): Promise<string> {
+	try {
+		const data = await response.json();
+		return data.message || data.error || JSON.stringify(data);
+	} catch {
+		return response.statusText || 'Unknown error';
+	}
+}
+
+/**
+ * Sleep utility for retry delays
+ */
+export function sleep(ms: number): Promise<void> {
+	return new Promise((resolve) => setTimeout(resolve, ms));
+}
+
+/**
+ * Check if error is retryable (network issues, 5xx errors)
+ */
+export function isRetryableError(error: ApiError): boolean {
+	if (error.code === 'NETWORK_ERROR' || error.code === 'TIMEOUT') {
+		return true;
+	}
+	if (error.status && error.status >= 500) {
+		return true;
+	}
+	return false;
+}
+
+/**
+ * Get base URL with runtime injection support for Docker
+ * Checks window.__PUBLIC_BACKEND_URL__ first, then falls back to provided URL
+ */
+export function getBaseUrl(configuredUrl: string): string {
+	if (typeof window !== 'undefined') {
+		const runtimeUrl = (window as unknown as Record<string, unknown>).__PUBLIC_BACKEND_URL__;
+		if (typeof runtimeUrl === 'string' && runtimeUrl) {
+			return runtimeUrl;
+		}
+	}
+	return configuredUrl;
+}