feat: Add user edit modal and user management pages

- Implemented user edit modal in user_edit.html for editing user details.
- Updated sidebar.html to correctly reflect active states for Users and Settings.
- Created table-07.html for displaying user data in a structured format.
- Added settings.html for managing email content and configurations.
- Developed users.html for listing all users with functionality to add and edit users.

api/users/add.php

@@ -0,0 +1,54 @@
+<?php
+require "../api.php";
+
+ini_set("display_errors", 1);
+ini_set("display_startup_errors", 1);
+error_reporting(E_ALL);
+
+$api = new spamhasiApi();
+$conf = $api->getConf();
+
+if (!$api->checkAuth()) {
+    header("Location: /users.html?status=500&error=Unauthorized");
+    exit;
+}
+
+if (!isset($_POST["name"]) || !isset($_POST["passwd1"]) || !isset($_POST["passwd2"])) {
+    header("Location: /users.html?status=500&error=Missing fields");
+    exit;
+}
+
+$name = htmlspecialchars($_POST["name"]);
+$passwd1 = hash("sha256", $_POST["passwd1"]);
+$passwd2 = hash("sha256", $_POST["passwd2"]);
+
+if (!preg_match('/^[a-z]+$/', $name)) {
+    header("Location: /users.html?status=500&error=Der Benutzername enthält ungültige Zeichen.");
+    exit;
+}
+
+if ($passwd1 !== $passwd2) {
+    header("Location: /users.html?status=500&error=Die Passwörter stimmen nicht überein.");
+    exit;
+}
+
+$db = $api->getDB();
+
+$sql = "INSERT INTO users (username, passwd) VALUES (:name, :passwd)";
+
+$stmt = $db->prepare($sql);
+
+$sql_exec = $stmt->execute([':name' => $name, ':passwd' => $passwd2]);
+
+if (!$sql_exec) {
+    header("Location: /users.html?status=500&error=SQL Error");
+}
+
+if (!file_put_contents($conf["PATH"] . "/tmp/user_sessions/" . $name . ".json", '{}')) {
+    header("Location: /users.html?status=500&error=Error to write session file.");
+    exit;
+}
+
+header("Location: /users.html?status=200");
+exit;
+?>