admin/index.php: add server-side pagination (25/page)

- Add Database::getThesesListCount(array $filters) — runs the same WHERE
  clauses as getThesesList() but with COUNT(DISTINCT t.id); used to compute
  total pages without loading all rows.
- Extend Database::getThesesList() with $limit/$offset parameters; when
  $limit > 0 appends LIMIT/OFFSET and re-binds positional params individually
  to avoid the PDO mixed-style restriction.
- Fix getThesesList() SELECT: add LEFT JOIN access_types + at.name as
  access_type — the column was referenced in the template but never fetched.
- Wire admin/index.php: read ?page=, compute $totalPages/$offset, pass
  $perPage=25 + $offset to getThesesList(); include pagination.php partial
  below the table with filter-preserving $baseParams.
- Add result-count line (<p class="admin-list-meta">) showing "X–Y sur Z TFE"
  when multiple pages exist.
- Add .admin-body .pagination-wrap / .pagination-btn / .pagination-info styles
  to admin.css (scoped to .admin-body to avoid colliding with public pages).

todo/02-php-components.md

@@ -10,7 +10,7 @@
 
 ## Shared UI partials — `templates/partials/`
 
-- [ ] **`pagination.php`** — pagination nav is duplicated between `index.php` and `search.php`; unify into one partial accepting `$page`, `$totalPages`, `$baseParams[]`
+- [x] **`pagination.php`** — partial created and used in both `search.php` and (now) `admin/index.php`; `admin/index.php` also gained proper server-side pagination (25/page) with filter-aware `$baseParams`
 - [ ] **`status-badge.php`** — published/pending badge + access badge pattern repeated in `index.php` admin table rows; extract into a partial
 - [ ] **`admin-alert.php`** — rename/merge `flash-messages.php` to also handle the 3 different legacy flash key patterns (`$_SESSION['error']`, `$_SESSION['admin_error']`, `$_SESSION['edit_error']`, etc.) that pages still consume manually instead of via `App::consumeFlash()`