feat: add creative welcome and external works square links

src/components/community/CommunityInvitation.tsx

@@ -0,0 +1,8 @@
+import { CommunityLink } from './CommunityLink';
+
+export function CommunityInvitation() {
+  return <section className="community-invitation" aria-label="作品广场入口" data-testid="community-invitation">
+    <div><h2>还没想到？去找找灵感吧</h2><p>作品广场里，有小伙伴们用麦洛做出的奇思妙想。</p></div>
+    <CommunityLink />
+  </section>;
+}

src/components/community/CommunityLink.tsx

@@ -0,0 +1,24 @@
+import { useState } from 'react';
+import { ArrowUpRight, Compass } from 'lucide-react';
+import { openCommunity } from '@/lib/community';
+import './community.css';
+
+export function CommunityLink({ variant = 'inline', collapsed = false }: {
+  variant?: 'inline' | 'sidebar'; collapsed?: boolean;
+}) {
+  const [opening, setOpening] = useState(false);
+  const [error, setError] = useState(false);
+  return <div>
+    <button type="button" className="community-link" data-variant={variant} data-collapsed={collapsed}
+      aria-label={variant === 'sidebar' ? '作品广场' : '去作品广场逛逛'}
+      title="在浏览器打开作品广场" disabled={opening}
+      onClick={() => {
+        setOpening(true); setError(false);
+        void openCommunity().catch(() => setError(true)).finally(() => setOpening(false));
+      }}>
+      <Compass aria-hidden="true" />
+      {!collapsed && <><span>{variant === 'sidebar' ? '作品广场' : '去作品广场逛逛'}</span><ArrowUpRight className="community-link-arrow" aria-hidden="true" /></>}
+    </button>
+    {error && <span className="community-link-error" role="alert">没能打开作品广场，请再点一次试试。</span>}
+  </div>;
+}

src/components/community/community.css

@@ -0,0 +1,36 @@
+.coding-chat-body { display: flex; flex: 1; flex-direction: column; min-height: 0; min-width: 0; overflow: hidden; }
+.coding-chat-body[hidden] { display: none; }
+.coding-chat-body[data-welcome="true"] { overflow-y: auto; padding: clamp(24px, 4vh, 48px) 24px 28px; background: radial-gradient(ellipse at 45% 18%, #fff8e8 0%, #fffdf8 28%, #fff 67%); }
+.coding-chat-body[data-welcome="true"] .classroom-chat-view { flex: 0 0 auto; }
+.coding-chat-body[data-welcome="true"] .classroom-composer-view { width: 100%; max-width: 740px; margin: 0 auto; }
+.coding-chat-body[data-welcome="true"] [data-testid="coding-message-composer"] { width: 100%; padding: 0 0 28px; }
+.coding-chat-body[data-welcome="true"] .chat-composer-surface { background: #fff; border-color: #d7dfda; border-radius: 20px; box-shadow: 0 5px 0 #eaf0e8, 0 12px 32px #69774b08; }
+.coding-start-heading { position: relative; width: 100%; max-width: 740px; margin: 0 auto; padding: 0 12px 24px; text-align: center; }
+.coding-start-mark { display: inline-grid; position: relative; place-items: center; width: 57px; height: 59px; border-radius: 18px; border: 1px solid #f2d6a7; background: #fff0d7; box-shadow: 0 4px 0 #eeddbd; transform: rotate(-7deg); animation: community-hello 650ms ease-out both; }
+.coding-start-mark img { width: 35px; height: 35px; }
+.coding-start-mark > svg { position: absolute; width: 17px; height: 17px; right: -24px; top: -2px; color: #c78b36; }
+.coding-start-mark > svg:last-child { width: 12px; height: 12px; left: -23px; top: 39px; color: #83a496; }
+.coding-start-eyebrow { margin: 18px 0 7px; color: #7a7769; font-size: 12px; letter-spacing: .08em; }
+.coding-start-heading h1 { color: #304968; font-size: clamp(24px, 2.5vw, 34px); line-height: 1.45; font-weight: 650; letter-spacing: -.04em; }
+.coding-start-heading h1 span { position: relative; white-space: nowrap; background: linear-gradient(transparent 73%, #ffe6a6 73%, #ffe6a6 94%, transparent 94%); }
+.coding-start-caption { margin-top: 10px; color: #718096; font-size: 13px; line-height: 1.8; }
+.community-invitation { display: flex; align-items: center; justify-content: space-between; gap: 18px; width: 100%; max-width: 740px; margin: 5px auto 0; padding: 21px 23px; border: 1px dashed #e4d9bc; border-radius: 18px; background: #fffaf0; color: #304968; }
+.community-invitation h2 { margin-bottom: 5px; font-size: 15px; font-weight: 600; }
+.community-invitation p { color: #7c806e; font-size: 12px; line-height: 1.7; }
+.community-link { display: inline-flex; align-items: center; justify-content: center; gap: 7px; min-height: 40px; padding: 8px 13px; border: 1px solid #dce5d0; border-radius: 12px; background: #f0f5e8; color: #526b46; font-size: 13px; cursor: pointer; white-space: nowrap; }
+.community-link:hover:not(:disabled) { background: #e5eed9; border-color: #b7c6a4; }
+.community-link:disabled { opacity: .6; cursor: wait; }
+.community-link:focus-visible { outline: 2px solid #547ab0; outline-offset: 3px; }
+.community-link svg { width: 17px; height: 17px; flex-shrink: 0; }
+.community-link .community-link-arrow { width: 14px; height: 14px; }
+.community-link[data-variant="sidebar"] { justify-content: flex-start; width: 100%; margin-top: 12px; border-color: transparent; background: transparent; text-align: left; }
+.community-link[data-variant="sidebar"]:hover { background: #e8f0e7; }
+.community-link[data-collapsed="true"] { justify-content: center; padding-inline: 0; }
+.community-link-error { display: block; margin-top: 6px; color: #965a45; font-size: 12px; line-height: 1.6; }
+@keyframes community-hello { 0% { transform: rotate(-15deg) translateY(5px); opacity: 0; } 70% { transform: rotate(3deg); opacity: 1; } 100% { transform: rotate(-7deg); } }
+@media (max-width: 600px) {
+  .coding-chat-body[data-welcome="true"] { padding: 24px 16px; }
+  .coding-start-caption { max-width: 230px; margin: 9px auto 0; }
+  .community-invitation { flex-direction: column; align-items: flex-start; gap: 13px; padding: 19px; }
+}
+@media (prefers-reduced-motion: reduce) { .coding-start-mark { animation: none; } }

src/components/layout/Sidebar.tsx

@@ -53,6 +53,7 @@ import { useProviderStore } from '@/stores/providers';
 import type { CodingProjectSummary } from '@/types/coding-project';
 import { useProjectConfigStore } from '@/stores/project-config';
 import { toast } from 'sonner';
+import { CommunityLink } from '@/components/community/CommunityLink';
 
 type OpenDialogResult = {
   canceled: boolean;
@@ -435,6 +436,7 @@ export function Sidebar({
           <Plus className="h-4 w-4 shrink-0 text-brand" />
           {!sidebarCollapsed && '新建项目'}
         </button>
+        <CommunityLink variant="sidebar" collapsed={sidebarCollapsed} />
         <div className="classroom-projects mt-3">
           <button
             type="button"