Move CSV import to inline dialog on list page

TODO.md

@@ -1,6 +1,12 @@
 # TODO
 
 ## Done
+- [x] Move CSV import from standalone import.php to inline dialog on the list page
+  - [x] Import logic embedded in index.php (processed before render)
+  - [x] `<dialog>` with form, results log, and auto-opens on post-submit
+  - [x] "Importer un CSV" button in list header row next to h1
+  - [x] Nav link to import.php removed; import.php now redirects to /admin/
+  - [x] CSS: `.admin-dialog`, `.admin-list-header`, `.admin-import-log`
 - [x] Create Paramètres page consolidating maintenance toggle and account settings into two sections
   - [x] New `public/admin/parametres.php` with Maintenance + Compte administrateur sections
   - [x] Nav updated: “Compte” replaced by “Paramètres” linking to `parametres.php`