Refactor admin pages to use shared head and navigation components

- Created `admin-head.php` for consistent <head> markup across admin pages.
- Created `admin-nav.php` for shared navigation bar, reducing duplication.
- Updated all admin pages (account, hours, index, login, menu, users) to utilize the new components.
- Added security headers to `auth.php` and `index.php` for improved security.
- Introduced `security-headers.php` to manage security headers across the application.
- Moved inline styles from admin pages to SCSS files to comply with Content Security Policy (CSP).
- Normalized file permissions during build process to prevent permission issues on deployment.

admin/login.php

@@ -2,6 +2,7 @@
 require_once __DIR__ . '/../inc/auth.php';
 require_once __DIR__ . '/../inc/login-throttle.php';
 require_once __DIR__ . '/../inc/assets.php';
+require_once __DIR__ . '/../inc/admin-head.php';
 
 $error = '';
 
@@ -27,15 +28,7 @@ if ($_SERVER['REQUEST_METHOD'] === 'POST') {
 ?>
 <!doctype html>
 <html lang="en">
-<head>
-  <meta charset="UTF-8">
-  <meta name="viewport" content="width=device-width, initial-scale=1">
-  <title>Admin Login | The Old Fitz Public House</title>
-  <link rel="preconnect" href="https://fonts.googleapis.com">
-  <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin>
-  <link href="https://fonts.googleapis.com/css2?family=Fraunces:wght@600&family=Karla:wght@400;500;600&family=IBM+Plex+Mono:wght@400;500&display=swap" rel="stylesheet">
-  <link rel="stylesheet" href="../styles.css<?= asset_version('styles.css') ?>">
-</head>
+<?php render_admin_head('Sign In'); ?>
 <body class="admin-login-body">
   <div class="login-card">
     <div class="login-header">