style: unify form element styles in common.css, redesign focus rings, refactor public search bar, tweak admin section

TODO.md

@@ -109,3 +109,21 @@
   - [x] All `$required = true` callers in `form.php`, `fieldset-tfe-info.php`, `fieldset-academic.php`, `fieldset-licence-explanation.php`, `fieldset-files.php` changed to `!$adminMode`
   - [x] Hardcoded `required` HTML attributes in `fieldset-tfe-info.php` (synopsis, objet radios), `fieldset-licence-explanation.php` (access type radios), `jury-fieldset.php` (promoteur, lecteurs interne/externe) gated on `!$adminMode`
   - [x] Dynamic JS `ulbInput.required` in jury fieldset also gated
+# TODO
+
+- [x] Make all heading font sizes the same (slightly smaller than current h1) in common.css
+- [x] Remove individual font-size overrides from other CSS files so they inherit
+- [x] Standardise header nav structure: admin uses nav-left/nav-right like public
+- [x] Unify font-size for all nav links (logo + nav links all use var(--step--1))
+- [x] Clean up redundant CSS rules (.nav-logo, .nav-left-links)
+- [x] Update admin.css selectors to match new header structure
+- [x] Bump nav font-size to var(--step-0)
+- [x] Add small inverted top gradient to admin body
+- [x] Commit
+- [x] Cap home page cards grid to max 3 columns (was auto-fill, now repeat(3, 1fr) with 2→1 column breakpoints)
+- [x] Remove Modifier link from admin header when on edit page
+- [x] Move admin nav links to right side, keep only logo on left
+- [x] Remove Mots-clés from admin header, add as button in dashboard toolbar; use grid layout (title|stats, search|buttons)
+- [x] Group admin toolbar buttons: + Ajouter + Mots-clés stacked above Import/Export
+- [x] Stack admin filters vertically: search+button row above dropdowns row
+- [x] Standardise form inputs/selects/textareas in common.css: padding, --radius var, 2px accent border on focus