feat(02-02): create login/registration page with responsive layout

- Add create_login_page() method to DDHH_JM_Pages class
- Combined view with registration form (Formidable shortcode) and login form (wp_login_form)
- German headings: "Neu registrieren" and "Bereits registriert?"
- Responsive two-column layout (desktop) with flexbox
- Stacked layout on mobile (< 768px)
- Inline CSS styling for visual separation and consistency
- Background colors and borders for section distinction
- Page accessible at /anbieter-login/
- Duplicate prevention: checks for existing page by slug

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

includes/class-pages.php

@@ -21,6 +21,9 @@ class DDHH_JM_Pages {
 	public static function create_provider_pages() {
 		// Create Anbieter Dashboard page
 		self::create_dashboard_page();
+
+		// Create Anbieter Login page
+		self::create_login_page();
 	}
 
 	/**
@@ -52,4 +55,133 @@ class DDHH_JM_Pages {
 			update_option( 'ddhh_jm_dashboard_page_id', $page_id );
 		}
 	}
+
+	/**
+	 * Create login/registration page
+	 */
+	private static function create_login_page() {
+		// Check if page already exists by slug
+		$existing_page = get_page_by_path( 'anbieter-login' );
+
+		if ( $existing_page ) {
+			// Page already exists, store ID if not stored
+			$stored_page_id = get_option( 'ddhh_jm_login_page_id' );
+			if ( ! $stored_page_id ) {
+				update_option( 'ddhh_jm_login_page_id', $existing_page->ID );
+			}
+			return;
+		}
+
+		// Get registration form ID
+		$registration_form_id = DDHH_JM_Formidable::get_registration_form_id();
+
+		// Build page content with inline CSS and two sections
+		$content = '<style>
+			.ddhh-auth-container {
+				display: flex;
+				gap: 2rem;
+				margin: 2rem 0;
+			}
+
+			.ddhh-register-section,
+			.ddhh-login-section {
+				flex: 1;
+				padding: 2rem;
+				background: #f9f9f9;
+				border-radius: 8px;
+				border: 1px solid #e0e0e0;
+			}
+
+			.ddhh-register-section h2,
+			.ddhh-login-section h2 {
+				margin-top: 0;
+				margin-bottom: 1.5rem;
+				color: #333;
+				font-size: 1.5rem;
+			}
+
+			/* Mobile responsive - stacked layout */
+			@media (max-width: 768px) {
+				.ddhh-auth-container {
+					flex-direction: column;
+				}
+			}
+
+			/* Form styling for consistency */
+			.ddhh-auth-container input[type="text"],
+			.ddhh-auth-container input[type="email"],
+			.ddhh-auth-container input[type="password"] {
+				width: 100%;
+				padding: 0.75rem;
+				margin-bottom: 1rem;
+				border: 1px solid #ddd;
+				border-radius: 4px;
+				box-sizing: border-box;
+			}
+
+			.ddhh-auth-container input[type="submit"],
+			.ddhh-auth-container button[type="submit"] {
+				background: #0073aa;
+				color: white;
+				padding: 0.75rem 1.5rem;
+				border: none;
+				border-radius: 4px;
+				cursor: pointer;
+				font-size: 1rem;
+			}
+
+			.ddhh-auth-container input[type="submit"]:hover,
+			.ddhh-auth-container button[type="submit"]:hover {
+				background: #005a87;
+			}
+		</style>';
+
+		$content .= '<div class="ddhh-auth-container">';
+
+		// Registration section
+		$content .= '<div class="ddhh-register-section">';
+		$content .= '<h2>Neu registrieren</h2>';
+		if ( $registration_form_id ) {
+			$content .= '[formidable id=' . $registration_form_id . ']';
+		} else {
+			$content .= '<p>Registrierungsformular wird geladen...</p>';
+		}
+		$content .= '</div>';
+
+		// Login section
+		$content .= '<div class="ddhh-login-section">';
+		$content .= '<h2>Bereits registriert?</h2>';
+
+		// Build wp_login_form args for German labels
+		$login_args = array(
+			'echo'           => false,
+			'redirect'       => home_url( '/anbieter-dashboard/' ),
+			'label_username' => 'E-Mail oder Benutzername',
+			'label_password' => 'Passwort',
+			'label_remember' => 'Angemeldet bleiben',
+			'label_log_in'   => 'Anmelden',
+		);
+
+		$content .= wp_login_form( $login_args );
+		$content .= '</div>';
+
+		$content .= '</div>'; // .ddhh-auth-container
+
+		// Create the login/registration page
+		$page_data = array(
+			'post_title'   => 'Anbieter Login',
+			'post_name'    => 'anbieter-login',
+			'post_content' => $content,
+			'post_status'  => 'publish',
+			'post_type'    => 'page',
+			'post_author'  => 1, // Admin user
+		);
+
+		$page_id = wp_insert_post( $page_data );
+
+		if ( $page_id && ! is_wp_error( $page_id ) ) {
+			// Store page ID in options
+			update_option( 'ddhh_jm_login_page_id', $page_id );
+		}
+	}
 }