refactor: adopt button in login page

Author: root

packages/web/src/components/ui/MIGRATION.md

@@ -2,7 +2,7 @@
 
 | Component | Status | Legacy classes | Callers left | Last update |
 |---|---|---|---:|---|
-| Button | ⚫ not-started | `.btn .btn-*` | 31 | 2026-05-06 |
+| Button | 🟡 in-flight | `.btn .btn-*` | 30 | 2026-05-06 |
 | IconButton | ⚫ not-started | `.btn` icon-only | — | — |
 | Input | ⚫ not-started | `.input` | — | — |
 | Textarea | ⚫ not-started | `.input.textarea` | — | — |

packages/web/src/components/ui/README.md

@@ -7,7 +7,9 @@
 - PC / 移动差异默认由 token 或共享内部逻辑解决，业务代码不直接写 `matchMedia`。
 
 ## 已实现组件
-当前 phase 只会先落 `Button`。公共导出完成后，这里会改成可用组件列表。
+| Component | Tier | Public API | Notes |
+|---|---|---|---|
+| Button | 0 | `src/components/ui/index.ts` named export only | `primary / secondary / ghost / danger` × `sm / md / lg` |
 
 ## 迁移状态
 见 `./MIGRATION.md`。

packages/web/src/features/auth/index.tsx

@@ -2,6 +2,7 @@ import { useAtom, useAtomValue } from "jotai";
 import { useEffect, useState } from "react";
 import { authenticatedAtom, localeAtom } from "../../atoms/app-ui";
 import { authEnabledAtom } from "../../atoms/connection";
+import { Button } from "../../components/ui";
 import { useViewport } from "../../hooks/use-viewport";
 import { formatDate, useTranslation } from "../../lib/i18n";
 
@@ -157,13 +158,15 @@ export function LoginPage() {
             onChange={(e) => setPassword(e.target.value)}
             placeholder={t("settings.auth.password")}
           />
-          <button
-            className="btn btn-primary btn-lg auth-submit"
+          <Button
+            className="auth-submit"
+            variant="primary"
+            size="lg"
             type="submit"
             disabled={checkingStatus || submitting || !password.trim()}
           >
             {submitLabel}
-          </button>
+          </Button>
         </form>
       </div>
     </div>