Extract last inline style from header.php into admin.css

The SVG icon in the admin nav's public-site link had two inline styles:
  style="vertical-align:middle;margin-right:0.4em"

Moved to a new CSS rule:
  .admin-body header nav > a svg { vertical-align: middle; margin-right: 0.4em; }

templates/header.php now contains zero style= attributes.
The only remaining inline styles project-wide are:
  - dynamic gradient (hsl computed from $item['id']) in public/index.php — legitimately dynamic
  - --disk-pct/--disk-color custom properties in system.php — carry PHP runtime values

TODO.md

@@ -11,6 +11,8 @@ Pending tasks have been split into topic files under [`todo/`](todo/README.md):
 
 ## Recently completed (this session)
 
+- [x] `templates/header.php` + `admin.css` — extracted last remaining inline `style=` from any shared template: `style="vertical-align:middle;margin-right:0.4em"` on the admin-nav public-site SVG icon moved to `.admin-body header nav > a svg` rule in `admin.css`; `templates/header.php` now contains zero `style=` attributes; only the dynamic gradient (`hsl(<?= $hue ?>)`) in `public/index.php` and the PHP-runtime `--disk-pct`/`--disk-color` custom properties in `system.php` remain (both legitimately dynamic)
+
 - [x] `admin/thanks.php` + `admin/pages.php` + `admin.css` — extracted last 3 inline `style=` attributes from admin PHP templates: `<div style="margin-top:1.5rem;display:flex;gap:.75rem;flex-wrap:wrap;">` in `thanks.php` → `class="admin-action-bar"` (`.admin-action-bar` rule added to CSS); `<p style="color:var(--text-secondary);">` in `thanks.php` → `class="admin-muted"` (`.admin-muted` rule added); `style="font-size:.8rem;padding:.3rem .75rem;"` on Éditer button in `pages.php` → `class="admin-btn admin-btn--sm"` (uses existing modifier). Only the dynamic `--disk-pct`/`--disk-color` CSS custom properties on the disk bar in `system.php` remain (carry PHP runtime values — legitimate).
 
 - [x] `variables.css` + `search.css` — public dark-mode support via `@media (prefers-color-scheme: dark)` scoped to `body:not(.admin-body)`: all semantic tokens (`--bg-*`, `--text-*`, `--border-*`, `--accent-*`, status colours) overridden with dark equivalents; `--accent-primary` lightened to `#b87fd4` for WCAG contrast on dark backgrounds; `--search-error-*` variables added to replace hardcoded `#fff0f0`/`#c00` in `.search-error`; admin pages unaffected

public/assets/css/admin.css

@@ -18,6 +18,12 @@
   opacity: 1;
 }
 
+/* Public-site link icon in admin nav */
+.admin-body header nav > a svg {
+  vertical-align: middle;
+  margin-right: 0.4em;
+}
+
 /* Active nav link — non-colour indicator required by WCAG 1.4.1 */
 .admin-body header nav ul a[aria-current="page"] {
   border-bottom: 2px solid currentColor;

templates/header.php

@@ -13,7 +13,7 @@ $_thesisId     = $_GET['id'] ?? null;
 
     <nav aria-label="Navigation admin">
         <a href="/" target="_blank" rel="noopener noreferrer">
-            <svg aria-hidden="true" xmlns="http://www.w3.org/2000/svg" width="16" height="16" fill="currentColor" viewBox="0 0 256 256" style="vertical-align:middle;margin-right:0.4em"><path d="M208,72H128V32a8,8,0,0,0-13.66-5.66l-96,96a8,8,0,0,0,0,11.32l96,96A8,8,0,0,0,128,224V184h80a16,16,0,0,0,16-16V88A16,16,0,0,0,208,72Zm0,96H120a8,8,0,0,0-8,8v28.69L35.31,128,112,51.31V80a8,8,0,0,0,8,8h88Z"></path></svg>Posterg<span class="sr-only"> (site public, nouvel onglet)</span>
+            <svg aria-hidden="true" xmlns="http://www.w3.org/2000/svg" width="16" height="16" fill="currentColor" viewBox="0 0 256 256"><path d="M208,72H128V32a8,8,0,0,0-13.66-5.66l-96,96a8,8,0,0,0,0,11.32l96,96A8,8,0,0,0,128,224V184h80a16,16,0,0,0,16-16V88A16,16,0,0,0,208,72Zm0,96H120a8,8,0,0,0-8,8v28.69L35.31,128,112,51.31V80a8,8,0,0,0,8,8h88Z"></path></svg>Posterg<span class="sr-only"> (site public, nouvel onglet)</span>
         </a>
         <ul>
             <li><a href="/admin/" <?= $_currentPage === 'index.php' ? 'aria-current="page"' : '' ?>>Liste des TFE</a></li>