refactor: extract templates from public/

- Created /templates for main site (header.php, footer.php)
- Created /templates/admin for admin section (head.php, footer.php)
- Removed /public/includes and /public/admin/inc
- Updated all references in code and docs
- Tests passing ✅

Cleaner separation: /public only contains web-accessible files (PHP entry points + assets)

public/memoire.php

@@ -29,7 +29,7 @@ if (isset($_GET['id'])) {
 }
 
 // Include the header template
-include APP_ROOT . '/public/includes/header.php'; ?>
+include APP_ROOT . '/templates/header.php'; ?>
 <main>
     <div class="item">
         <div class="card-content">
@@ -151,4 +151,4 @@ include APP_ROOT . '/public/includes/header.php'; ?>
 </main>
 
 <!-- Include the footer template -->
-<?php include APP_ROOT . '/public/includes/footer.php'; ?>
+<?php include APP_ROOT . '/templates/footer.php'; ?>