feat(portal): 고객 포털 인증과 소셜 로그인 기반 추가

TaxBaik.Web/Pages/Portal/Register.cshtml

@@ -0,0 +1,35 @@
+@page "/portal/register"
+@model TaxBaik.Web.Pages.Portal.RegisterModel
+@{
+    ViewData["Title"] = "고객 포털 회원가입";
+    ViewData["Description"] = "고객 포털 회원가입 페이지입니다.";
+    ViewData["CanonicalUrl"] = $"{Request.Scheme}://{Request.Host}/taxbaik/portal/register";
+}
+
+<section class="container py-5" style="max-width: 640px;">
+    <h1 class="h3 fw-bold mb-4">고객 포털 회원가입</h1>
+    <div class="alert alert-secondary">
+        가입 흐름은 다음 단계에서 이메일/전화번호 검증과 소셜 로그인으로 확장합니다.
+    </div>
+    <form method="post" class="row g-3">
+        <div class="col-md-6">
+            <label class="form-label">이름</label>
+            <input class="form-control" asp-for="Name" />
+        </div>
+        <div class="col-md-6">
+            <label class="form-label">연락처</label>
+            <input class="form-control" asp-for="Phone" />
+        </div>
+        <div class="col-12">
+            <label class="form-label">이메일</label>
+            <input class="form-control" asp-for="Email" />
+        </div>
+        <div class="col-12">
+            <label class="form-label">비밀번호</label>
+            <input class="form-control" asp-for="Password" type="password" />
+        </div>
+        <div class="col-12">
+            <button class="btn btn-dark" type="submit">가입하기</button>
+        </div>
+    </form>
+</section>