Extract apropos contacts/credits to config/apropos.php

Names, roles, emails, and credits on the À propos page were hardcoded
directly in apropos.php HTML. To update a contact meant editing a
template file — risky for non-developers and easy to introduce a typo
or broken mailto link.

Changes:
- config/apropos.php: new config array with erg_url, contacts[] (name,
  role, email per person) and credits[] (label/value pairs); follows
  the same pattern as config/admin_credentials.php
- public/apropos.php: loads config via require; aside section now loops
  over $apropos['contacts'] and $apropos['credits'] with htmlspecialchars
  throughout; hardcoded HTML strings removed entirely

Also audited todo/02-php-components.md and marked 8 stale items as done:
all 5 form field partials were already implemented and in use, the
flash-message consolidation was already handled by App::consumeFlash(),
and the RateLimit cache dir was already at storage/cache/rate_limit
(excluded from deploy rsync).

config/apropos.php

@@ -0,0 +1,53 @@
+<?php
+
+/**
+ * À propos page — contacts and credits configuration.
+ *
+ * Edit this file to update the people listed in the Contacts and Crédits
+ * sections of the public "À propos" page without touching the template.
+ *
+ * contacts[] — each entry:
+ *   'name'  string  Full display name
+ *   'role'  string  Short description of role (plain text, no HTML)
+ *   'email' string  Email address (used for mailto: link)
+ *
+ * credits[] — each entry:
+ *   'label' string  Credit category / title (e.g. "Design & développement")
+ *   'value' string  Free-text value; HTML entities will be escaped, so use
+ *                   plain text (ampersands written as "&", not "&amp;")
+ *
+ * erg_url — URL for the "Site de l'erg" link in the aside.
+ */
+
+return [
+    'erg_url' => 'https://erg.be',
+
+    'contacts' => [
+        [
+            'name'  => 'Laurent Leprince',
+            'role'  => 'Bibliothèque d'architecture, d'ingénierie architecturale, d'urbanisme (BAIU) :',
+            'email' => 'laurent.leprince@uclouvain.be',
+        ],
+        [
+            'name'  => 'Xavier Gorgol',
+            'role'  => 'Responsable des mémoires de l'ERG :',
+            'email' => 'xavier.gorgol@erg.be',
+        ],
+        [
+            'name'  => 'Brigitte Ledune',
+            'role'  => 'Cours de suivi de mémoire :',
+            'email' => 'brigitte.ledune@erg.be',
+        ],
+    ],
+
+    'credits' => [
+        [
+            'label' => 'Design & développement',
+            'value' => 'Olivia Marly, Théophile Gerveau-Mercie & Théo Hennequin',
+        ],
+        [
+            'label' => 'Typographies',
+            'value' => 'Ductus (Amélie Dumont) & BBB DM Sans',
+        ],
+    ],
+];