feat(HAI-095): add authentication settings UI with backend API

- Add backend auth API endpoints (GET/PUT) with validation in routes.ts
- Create frontend API client functions for fetching and updating auth config
- Add Authentication Settings section to SettingsModal with token input form
- Add comprehensive tests for routes, API client, and SettingsModal components
- Wire up auth settings routes in dashboard server

packages/dashboard/src/server.ts

@@ -3,6 +3,7 @@ import { join, dirname } from "node:path";
 import { existsSync } from "node:fs";
 import { fileURLToPath } from "node:url";
 import type { TaskStore, MergeResult } from "@hai/core";
+import type { AuthStorageLike } from "./routes.js";
 import { createApiRoutes } from "./routes.js";
 import { createSSE } from "./sse.js";
 import { rateLimit, RATE_LIMITS } from "./rate-limit.js";
@@ -14,6 +15,8 @@ export interface ServerOptions {
   onMerge?: (taskId: string) => Promise<MergeResult>;
   /** Maximum concurrent worktrees / execution slots (default 2) */
   maxConcurrent?: number;
+  /** Optional AuthStorage instance for auth routes — if not provided, one is created internally */
+  authStorage?: AuthStorageLike;
 }
 
 export function createServer(store: TaskStore, options?: ServerOptions): ReturnType<typeof express> {