chore: 将后端移动到 api/ 目录，准备合并为单仓库

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

api/static/admin/css/login.css

@@ -0,0 +1,61 @@
+/* LOGIN FORM */
+
+.login {
+    background: var(--darkened-bg);
+    height: auto;
+}
+
+.login #header {
+    height: auto;
+    padding: 15px 16px;
+    justify-content: center;
+}
+
+.login #header h1 {
+    font-size: 1.125rem;
+    margin: 0;
+}
+
+.login #header h1 a {
+    color: var(--header-link-color);
+}
+
+.login #content {
+    padding: 20px;
+}
+
+.login #container {
+    background: var(--body-bg);
+    border: 1px solid var(--hairline-color);
+    border-radius: 4px;
+    overflow: hidden;
+    width: 28em;
+    min-width: 300px;
+    margin: 100px auto;
+    height: auto;
+}
+
+.login .form-row {
+    padding: 4px 0;
+}
+
+.login .form-row label {
+    display: block;
+    line-height: 2em;
+}
+
+.login .form-row #id_username, .login .form-row #id_password {
+    padding: 8px;
+    width: 100%;
+    box-sizing: border-box;
+}
+
+.login .submit-row {
+    padding: 1em 0 0 0;
+    margin: 0;
+    text-align: center;
+}
+
+.login .password-reset-link {
+    text-align: center;
+}