fix(web): 注册页补充已登录重定向守卫，与登录页 / classic 主题保持一致 (#5908)

[Heykode]

📝 变更描述 / Description

default 主题下，登录页 /sign-in 的 route 已在 beforeLoad 中做了"已登录则重定向到 /dashboard"的守卫，但注册页 /sign-up（以及其别名 /register，后者仅 throw redirect 到 /sign-up）没有等价守卫，导致已登录用户访问注册页时停在注册表单，而非进入主界面。

本 PR 在 sign-up.tsx 的 route 增加与 sign-in.tsx 一致的 beforeLoad 守卫：沿用同一 useAuthStore 判断登录态，已登录时 throw redirect({ to: '/dashboard' })。守卫加在实际渲染注册页的 /sign-up，因此 /register 与 /sign-up 两个入口都被覆盖。该行为与旧 classic 主题 web/classic/src/helpers/auth.jsx 中 AuthRedirect 对 /register 的处理一致。

说明：这不是 rc.13→rc.16 之间的代码回归（两个 tag 的该路由文件除格式化外无功能差异，/sign-up 守卫在 default 前端自 v1.0 起从未存在），因此作为"行为一致性补齐"提交，归类为 Refactor / 一致性修复而非 Bug。

🚀 变更类型 / Type of change

• ⚡ 性能优化 / 重构 (Refactor) - 补齐注册页与登录页 / classic 主题一致的已登录重定向行为

🔗 关联任务 / Related Issue

• Closes default 主题注册页缺少已登录重定向守卫（与登录页 / classic 主题行为不一致） #5908

✅ 提交前检查项 / Checklist

• 人工确认: 我已亲自整理并撰写此描述。（另见下方 AI 协助声明）
• 非重复提交: 我已搜索现有 Issues 与 PRs，确认不是重复提交。
• Bug fix 说明: 本 PR 未标记为 Bug fix；已如实说明这是行为一致性补齐而非回归。
• 变更理解: 我已理解这些更改的工作原理及影响。
• 范围聚焦: 本 PR 仅改动 sign-up.tsx 一处，逻辑复用现有 sign-in.tsx 模式，无无关改动。
• 本地验证: 已本地 bun run typecheck 通过；bunx oxlint 对本文件零 error；format:check 通过。
• 安全合规: 无敏感凭据，符合项目规范。

📸 运行证明 / Proof of Work

• 对照实现：web/default/src/routes/(auth)/sign-in.tsx:32-41 已有等价守卫（跳 /dashboard）。
• 本 PR diff（sign-up.tsx）：新增 redirect / useAuthStore import，并在 route 增加 beforeLoad：

  beforeLoad: async () => {
    const { auth } = useAuthStore.getState()
    // 如果已经有用户信息，说明已登录，注册页对其无意义，跳转到 dashboard
    if (auth.user) {
      throw redirect({ to: '/dashboard' })
    }
  },

• 本地校验：bun run typecheck（tsgo -b）通过；bunx oxlint -c .oxlintrc.json "src/routes/(auth)/sign-up.tsx" 零 error；format 检查通过。

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AI 协助声明: 本 PR 的问题定位、根因分析与代码改动在 AI（Claude）辅助下完成，所有结论均经源码与 git 历史核对，并已本地 typecheck / lint 验证。提交者非本仓库历史核心开发者，特此声明。

Summary by CodeRabbit

• Bug Fixes
  • Signed-in users are now redirected away from the sign-up page to the dashboard.
  • Prevents authenticated users from accessing a page meant for new account creation.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: e4dd4c4a-9f56-4023-ba48-69c3f5ec5eab

📥 Commits

Reviewing files that changed from the base of the PR and between 1ae7574 and ebdbd96.

📒 Files selected for processing (1)

• web/default/src/routes/(auth)/sign-up.tsx

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Walkthrough

The sign-up route in the default theme adds a beforeLoad guard that checks authentication state via useAuthStore and redirects already-authenticated users to /dashboard, aligning its behavior with the existing sign-in route.

Changes

Sign-up authentication guard

Layer / File(s)	Summary
Add beforeLoad redirect guard web/default/src/routes/(auth)/sign-up.tsx	Imports redirect and useAuthStore; adds an async beforeLoad hook that throws a redirect to /dashboard if auth.user is present.

Estimated code review effort: 1 (Trivial) | ~3 minutes

Poem

A bunny hops to sign-up's door,
But finds a guard it hadn't before—
"Already in?" the guard will say,
"Then hop along to dashboard, stray!" 🐇
One small check, one tidy fix,
Consistency in the mix!

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly describes the sign-up redirect guard added for logged-in users and matches the main change.
Linked Issues check	✅ Passed	The change satisfies #5908 by adding an authenticated-user redirect on the default theme sign-up route to /dashboard.
Out of Scope Changes check	✅ Passed	The PR is narrowly scoped to the requested sign-up auth redirect and introduces no unrelated changes.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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