refactor(frontend): extract shared stores and components into packages

- Create @multica/fetch package for HTTP client and URL config
- Migrate hub store and hub-init hook to @multica/store
- Move HubSidebar component to @multica/ui for web/desktop reuse
- Update web app imports to use shared packages
- Remove counter store example and its component-example usage

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

packages/fetch/src/config.ts

@@ -0,0 +1,15 @@
+let consoleUrl = "http://localhost:4000"
+let gatewayUrl = "http://localhost:3000"
+
+export function setConfig(config: { consoleUrl?: string; gatewayUrl?: string }) {
+  if (config.consoleUrl) consoleUrl = config.consoleUrl
+  if (config.gatewayUrl) gatewayUrl = config.gatewayUrl
+}
+
+export function getConsoleUrl(): string {
+  return consoleUrl
+}
+
+export function getGatewayUrl(): string {
+  return gatewayUrl
+}

packages/fetch/src/http-client.ts

@@ -0,0 +1,28 @@
+import { getConsoleUrl } from "./config"
+
+export class HttpError extends Error {
+  constructor(
+    public status: number,
+    public statusText: string,
+  ) {
+    super(`HTTP ${status}: ${statusText}`)
+  }
+}
+
+async function request<T>(method: string, path: string, body?: unknown): Promise<T> {
+  const res = await fetch(`${getConsoleUrl()}${path}`, {
+    method,
+    headers: body ? { "Content-Type": "application/json" } : undefined,
+    body: body ? JSON.stringify(body) : undefined,
+  })
+  if (!res.ok) throw new HttpError(res.status, res.statusText)
+  return res.json()
+}
+
+/** Console REST API */
+export const consoleApi = {
+  get: <T>(path: string) => request<T>("GET", path),
+  post: <T>(path: string, body?: unknown) => request<T>("POST", path, body),
+  put: <T>(path: string, body: unknown) => request<T>("PUT", path, body),
+  delete: <T>(path: string) => request<T>("DELETE", path),
+}

packages/fetch/src/index.ts

@@ -0,0 +1,2 @@
+export { setConfig, getConsoleUrl, getGatewayUrl } from "./config"
+export { consoleApi, HttpError } from "./http-client"