Refactor admin panel: enhance user management and security features

- Added role-based access control for user management links in admin navigation.
- Improved user account display with a dedicated account link.
- Implemented form submission confirmation for delete actions in the admin interface.
- Introduced a password visibility toggle on the login page.
- Added login throttling to prevent brute-force attacks, recording failed attempts.
- Created a CLI script for creating an admin user, replacing the previous hardcoded admin credentials.
- Updated database schema to support login attempt tracking.
- Enhanced user editing functionality, allowing role changes with restrictions.
- Improved modal handling for user actions, ensuring better focus management.
- Added styles for new account management page and improved modal transitions.

bin/.htaccess

@@ -0,0 +1 @@
+Require all denied

bin/create-user.php

@@ -0,0 +1,53 @@
+<?php
+declare(strict_types=1);
+
+/**
+ * CLI-only: create an admin account.
+ *
+ * Replaces the old admin/password seed in inc/db.php. Run inside the
+ * container as www-data, so a newly created fitz.sqlite isn't owned by root:
+ *   docker exec -it -u www-data the-old-fitz php /var/www/html/bin/create-user.php
+ */
+
+if (PHP_SAPI !== 'cli') {
+	http_response_code(404);
+	exit;
+}
+
+require_once __DIR__ . '/../inc/users.php';
+
+function prompt(string $label, bool $hidden = false): string {
+	fwrite(STDOUT, $label);
+	if ($hidden) {
+		shell_exec('stty -echo');
+	}
+	$value = fgets(STDIN);
+	if ($hidden) {
+		shell_exec('stty echo');
+		fwrite(STDOUT, PHP_EOL);
+	}
+	return trim((string) $value);
+}
+
+$username = prompt('Username: ');
+if ($username === '') {
+	fwrite(STDERR, "Username is required.\n");
+	exit(1);
+}
+if (username_exists($username)) {
+	fwrite(STDERR, "User '$username' already exists.\n");
+	exit(1);
+}
+
+$password = prompt('Password (' . MIN_PASSWORD_LENGTH . '+ chars): ', true);
+if (strlen($password) < MIN_PASSWORD_LENGTH) {
+	fwrite(STDERR, 'Password must be at least ' . MIN_PASSWORD_LENGTH . " characters.\n");
+	exit(1);
+}
+if (prompt('Confirm password: ', true) !== $password) {
+	fwrite(STDERR, "Passwords don't match.\n");
+	exit(1);
+}
+
+$id = create_user($username, $password, 'admin');
+fwrite(STDOUT, "Created admin '$username' (id $id).\n");