Fix admin CSS not loading and quirks mode issues

Fixed multiple issues in admin panel:

1. CSS path: modern-normalize.css → modern-normalize.min.css
   (File is actually named .min.css)

2. Icon path: assets/icon.svg → /assets/admin_favicon.svg
   (Was relative, now absolute; correct filename)

3. Navigation: /admin/list.php → /admin/
   (list.php was renamed to index.php)

4. Short PHP tags: <? → <?php
   (Better compatibility, some servers don't enable short_open_tag)

5. Quirks mode warning was due to CSS not loading, not DOCTYPE
   (DOCTYPE was already present)

Files modified:
- public/admin/inc/head.php (main fixes)
- public/admin/index.php (short tags)
- public/admin/add.php (short tags)
- public/admin/import.php (short tags)

Need to redeploy for production: just deploy

public/assets/common.css

@@ -0,0 +1,105 @@
+@font-face {
+  font-family: police1;
+  src: url("./fonts/Combinedd.otf");
+}
+
+/* Dark theme */
+/* UTILE POUR FORCER UN MODE LIGHT */
+/* @media (prefers-color-scheme: dark) { */
+/* :root, */
+/* ::backdrop { */
+/* --bg: #fff; */
+/* --accent-bg: #f5f7ff; */
+/* --text: #212121; */
+/* --text-light: #585858; */
+/* --border: #898ea4; */
+/* --accent: #0d47a1; */
+/* --code: #d81b60; */
+/* --preformatted: #444; */
+/* --marked: #ffdd33; */
+/* --disabled: #efefef; */
+/* } */
+/* } */
+
+body {
+  background-color: white;
+  margin: 0;
+}
+
+/* FORMULAIRE */
+form label {
+  font-family: police1;
+  font-size: 1rem;
+}
+form input,
+select,
+textarea {
+  border-color: #c104fc;
+  overflow: visible;
+  outline: none;
+  background-color: white;
+}
+
+form input:focus,
+select:focus {
+  border: 3px solid rgba(77, 168, 112, 1);
+}
+
+label {
+  margin-top: 2rem;
+}
+
+input {
+  /* font-family: police1; */
+  /* font-weight: bold; */
+  background-color: none;
+  color: rgb(193, 4, 252);
+  border: 1px solid rgb(193, 4, 252);
+}
+
+a {
+  color: rgb(193, 4, 252);
+}
+
+a:hover {
+  text-decoration: none;
+}
+a, a:visited {
+  color: rgb(193, 4, 252);
+}
+
+input:active {
+  border-color: rgba(77, 168, 112, 1);
+}
+
+button,
+[role="button"],
+input[type="submit"],
+input[type="reset"],
+input[type="button"],
+label[type="button"] {
+  background-color: white;
+  margin-top: 2rem;
+  font-size: 16px;
+  border-radius: 10px;
+  padding: 2ch;
+  margin: 1rem;
+  a {
+    color: black;
+    text-decoration: none;
+  }
+}
+
+button {}
+
+/* For Google Chrome, Safari, and newer versions of Opera */
+::placeholder {
+  /* color: rgb(213, 73, 255); */
+  font-size: 0.8rem;
+}
+
+/* For Mozilla Firefox */
+::-moz-placeholder {
+  /* color: rgb(213, 73, 255); */
+  font-size: 0.8rem;
+}