feat(auth): redesign auth UI to match Dart original

- Full-bleed bg_login.png background outside 500px MobileShell
- Facebook landing: logo + Facebook pill button + "Other Sign In Options" link
- Replace centered Dialog with true bottom sheet (drag handle, top radius 28px)
- Email panel: internal login/register toggle, no separate route
- Pink gradient primary button (#f96ADE → #f657A0)
- Pill input fields (46px, white, radius 24, pink 10% shadow)
- Pink circular checkbox + bold Privacy/Terms rich text (visual only, non-blocking)
- Floating 40x40 white back button (top:20/left:20)
- Wire AuthPanelModeChanged dispatch for panel switching
- New design tokens (--color-auth-*, --auth-*, --radius-bottom-sheet)
- New generic BottomSheet component
- Copy ic-logo-login.png (+@2x, +@3x) from Dart assets

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/app/auth/components/email-register-form.tsx

@@ -3,6 +3,13 @@
  * 邮箱注册表单
  *
  * 原始 Dart: lib/ui/auth/widgets/email_register_form.dart
+ *
+ * 视觉规格（与 Dart 对齐）：
+ *   - 4 字段：username / email / password / confirmPassword（顺序与 Dart 一致）
+ *   - 字段无 label（仅 placeholder）
+ *   - 错误仅以红色横幅显示（AuthErrorMessage），无字段级错误
+ *   - 切换链接由父级 AuthEmailPanel 渲染
+ *   - 提交派发 `AuthEmailRegisterSubmitted`
  */
 import { useState } from "react";
 
@@ -20,13 +27,11 @@ import { AuthErrorMessage } from "./auth-error-message";
 import styles from "./email-form.module.css";
 
 export interface EmailRegisterFormProps {
-  onSwitchToLogin: () => void;
   globalError?: string | null;
   isLoading?: boolean;
 }
 
 export function EmailRegisterForm({
-  onSwitchToLogin,
   globalError,
   isLoading,
 }: EmailRegisterFormProps) {
@@ -35,25 +40,13 @@ export function EmailRegisterForm({
   const [password, setPassword] = useState("");
   const [username, setUsername] = useState("");
   const [confirmPassword, setConfirmPassword] = useState("");
-  const [errors, setErrors] = useState<
-    Partial<Record<"email" | "password" | "username" | "confirmPassword", string>>
-  >({});
 
   const submit = () => {
     const emailErr = validateEmail(email);
     const passwordErr = validatePassword(password);
     const usernameErr = validateUsername(username);
     const confirmErr = validateConfirmPassword(password, confirmPassword);
-    if (emailErr || passwordErr || usernameErr || confirmErr) {
-      setErrors({
-        email: emailErr ?? undefined,
-        password: passwordErr ?? undefined,
-        username: usernameErr ?? undefined,
-        confirmPassword: confirmErr ?? undefined,
-      });
-      return;
-    }
-    setErrors({});
+    if (emailErr || passwordErr || usernameErr || confirmErr) return;
     dispatch({
       type: "AuthEmailRegisterSubmitted",
       email,
@@ -71,53 +64,38 @@ export function EmailRegisterForm({
         submit();
       }}
     >
-      <AuthErrorMessage message={globalError ?? null} />
       <AuthTextField
-        label="Username"
         value={username}
         onChange={setUsername}
-        placeholder="cozsweet_user"
+        placeholder="Username"
         autoComplete="username"
-        errorMessage={errors.username ?? null}
       />
       <AuthTextField
-        label="Email"
         type="email"
         value={email}
         onChange={setEmail}
-        placeholder="you@example.com"
+        placeholder="Email"
         autoComplete="email"
-        errorMessage={errors.email ?? null}
       />
       <AuthTextField
-        label="Password"
         type="password"
         value={password}
         onChange={setPassword}
-        placeholder="••••••••"
+        placeholder="Password"
         autoComplete="new-password"
-        errorMessage={errors.password ?? null}
       />
       <AuthTextField
-        label="Confirm Password"
         type="password"
         value={confirmPassword}
         onChange={setConfirmPassword}
-        placeholder="••••••••"
+        placeholder="Confirm Password"
         autoComplete="new-password"
-        errorMessage={errors.confirmPassword ?? null}
         onSubmit={submit}
       />
+      <AuthErrorMessage message={globalError ?? null} />
       <AuthPrimaryButton type="submit" isLoading={isLoading}>
-        Create Account
+        Register
       </AuthPrimaryButton>
-      <button
-        type="button"
-        className={styles.linkButton}
-        onClick={onSwitchToLogin}
-      >
-        Already have an account? <span className={styles.link}>Log in</span>
-      </button>
     </form>
   );
 }