feat(HAI-001): add API rate limiting and replace emojis with Lucide icons

- Add rate limiting middleware to dashboard API endpoints
- Install lucide-react and replace emoji usage with Lucide icons across dashboard components
- Add rate limiter unit tests
- Document API rate limiting in README
- Refactor engine executor/triage and remove unused reviewer module

packages/dashboard/app/components/Header.tsx

@@ -1,3 +1,5 @@
+import { Settings } from "lucide-react";
+
 interface HeaderProps {
   onOpenSettings?: () => void;
 }
@@ -11,7 +13,7 @@ export function Header({ onOpenSettings }: HeaderProps) {
       </div>
       <div className="header-actions">
         <button className="btn-icon" onClick={onOpenSettings} title="Settings">
-          ⚙
+          <Settings size={16} />
         </button>
       </div>
     </header>

packages/dashboard/app/components/InlineCreateCard.tsx

@@ -1,4 +1,5 @@
 import { useState, useCallback, useEffect, useRef } from "react";
+import { Link } from "lucide-react";
 import type { Task, TaskCreateInput } from "@hai/core";
 import type { ToastType } from "../hooks/useToast";
 
@@ -77,7 +78,7 @@ export function InlineCreateCard({ tasks, onSubmit, onCancel, addToast }: Inline
             className="btn btn-sm dep-trigger"
             onClick={() => setShowDeps((v) => !v)}
           >
-            ⛓{dependencies.length > 0 ? ` ${dependencies.length} deps` : " Deps"}
+            <Link size={12} style={{ verticalAlign: 'middle' }} />{dependencies.length > 0 ? ` ${dependencies.length} deps` : " Deps"}
           </button>
           {showDeps && (
             <div className="dep-dropdown">

packages/dashboard/app/components/TaskCard.tsx

@@ -1,4 +1,5 @@
 import { useCallback, useState } from "react";
+import { Link, Clock } from "lucide-react";
 import type { Task, TaskDetail, Column } from "@hai/core";
 import { fetchTaskDetail } from "../api";
 import type { ToastType } from "../hooks/useToast";
@@ -80,10 +81,10 @@ export function TaskCard({ task, queued, onOpenDetail, addToast }: TaskCardProps
         <div className="card-meta">
           {task.dependencies && task.dependencies.length > 0 && (
             <span className="card-dep-badge">
-              ⛓ {task.dependencies.length} dep{task.dependencies.length > 1 ? "s" : ""}
+              <Link size={12} style={{ verticalAlign: 'middle' }} /> {task.dependencies.length} dep{task.dependencies.length > 1 ? "s" : ""}
             </span>
           )}
-          {queued && <span className="queued-badge">⏳ Queued</span>}
+          {queued && <span className="queued-badge"><Clock size={12} style={{ verticalAlign: 'middle' }} /> Queued</span>}
         </div>
       )}
     </div>

packages/dashboard/app/components/WorktreeGroup.tsx

@@ -1,4 +1,5 @@
 import type { Task, TaskDetail } from "@hai/core";
+import { ClipboardList, GitBranch } from "lucide-react";
 import { TaskCard } from "./TaskCard";
 import type { ToastType } from "../hooks/useToast";
 
@@ -21,7 +22,7 @@ export function WorktreeGroup({
     <div className="worktree-group">
       <div className="worktree-group-header">
         <span className="worktree-icon">
-          {label === "Up Next" || label === "Unassigned" ? "📋" : "🌿"}
+          {label === "Up Next" || label === "Unassigned" ? <ClipboardList size={14} /> : <GitBranch size={14} />}
         </span>
         <span className="worktree-label">{label}</span>
       </div>