Redesign UI to match target design images

- Flat purple-gradient nav bar with POSTERG/RÉPERTOIRE/À PROPOS links
- Full-width search bar with icon, bottom-border only, below nav
- Home: white bg, media card grid (thumbnail + author/title label below)
- Répertoire: 4-column index (Années/Catégories/Étudiantes/Mots-clés)
- TFE: 2-column layout (large text left, media right)
- À Propos: 2-column, large monospace text, new apropos.php page
- Admin: dark theme (#1a1a1a), purple gradient nav, bottom-border inputs
- New shared partials: templates/nav.php, templates/search-bar.php
- Rewrote all CSS: common, main, search, tfe, apropos, admin

public/assets/apropos.css

@@ -0,0 +1,139 @@
+/* ============================================================
+   À PROPOS PAGE (apropos.php)
+   ============================================================ */
+
+html, body {
+  margin: 0;
+  padding: 0;
+  height: 100%;
+}
+
+.apropos-body {
+  display: flex;
+  flex-direction: column;
+  min-height: 100vh;
+  background: var(--white);
+}
+
+.apropos-main {
+  flex: 1;
+  overflow-y: auto;
+  padding: 2.5rem 1.5rem 4rem;
+}
+
+/* Two-column layout */
+.apropos-layout {
+  display: grid;
+  grid-template-columns: 1.4fr 1fr;
+  gap: 4rem;
+  max-width: 1200px;
+}
+
+/* Left col — main description text in big monospace */
+.apropos-left {}
+
+.apropos-description {
+  font-family: "Courier New", Courier, monospace;
+  font-size: 1.55rem;
+  line-height: 1.45;
+  color: var(--black);
+  font-weight: 400;
+  margin: 0 0 2rem 0;
+}
+
+.apropos-description p {
+  margin: 0 0 1.2em 0;
+}
+
+/* Right col — links, contacts, credits */
+.apropos-right {
+  display: flex;
+  flex-direction: column;
+  gap: 2rem;
+}
+
+.apropos-section-title {
+  font-family: "Courier New", Courier, monospace;
+  font-size: 1.55rem;
+  font-weight: 400;
+  color: var(--black);
+  margin: 0 0 0.5rem 0;
+  line-height: 1.2;
+}
+
+.apropos-section-title a {
+  color: inherit;
+  text-decoration: underline;
+  text-underline-offset: 3px;
+}
+
+.apropos-contact {
+  margin-bottom: 1rem;
+}
+
+.apropos-contact-name {
+  font-weight: 700;
+  font-size: 0.95rem;
+  color: var(--black);
+  display: block;
+  margin-bottom: 0.15rem;
+}
+
+.apropos-contact-role,
+.apropos-contact-email {
+  font-size: 0.9rem;
+  color: var(--black);
+  line-height: 1.4;
+  display: block;
+}
+
+.apropos-credits-text {
+  font-size: 0.9rem;
+  color: var(--black);
+  line-height: 1.6;
+}
+
+/* Licences section */
+.apropos-licences {
+  margin-top: 2rem;
+}
+
+.apropos-licences h2 {
+  font-family: "Courier New", Courier, monospace;
+  font-size: 1.55rem;
+  font-weight: 400;
+  margin: 0 0 0.75rem 0;
+}
+
+.apropos-licences p {
+  font-size: 0.9rem;
+  color: var(--black);
+  line-height: 1.6;
+  margin: 0 0 0.75rem 0;
+}
+
+/* Responsive */
+@media (max-width: 900px) {
+  .apropos-layout {
+    grid-template-columns: 1fr;
+    gap: 2rem;
+  }
+
+  .apropos-description {
+    font-size: 1.2rem;
+  }
+
+  .apropos-section-title {
+    font-size: 1.2rem;
+  }
+}
+
+@media (max-width: 600px) {
+  .apropos-main {
+    padding: 1.5rem 1rem 3rem;
+  }
+
+  .apropos-description {
+    font-size: 1rem;
+  }
+}