semantic HTML: apropos.php and licence.php (TODO section V & VI)

apropos.php:
- Remove redundant <div class="apropos-left"> wrapper; prose div is now a direct
  grid child
- <div class="apropos-description apropos-page-content"> → <div class="prose">
  (single canonical class for Markdown-rendered content)
- <div class="apropos-right"> → <aside class="apropos-aside"> (supplementary info
  landmark; contacts and credits are secondary to the main description)
- Three bare <div> wrappers inside the aside → <section> (erg link, Contacts, Crédits)
- Three <div class="apropos-contact"> entries → <address> with font-style:normal
  override; <span class="apropos-contact-name"> → <strong>;
  <span class="apropos-contact-email"> → <a href="mailto:…">
  Removes classes: apropos-left, apropos-right, apropos-contact, apropos-contact-name,
  apropos-contact-role, apropos-contact-email, apropos-description, apropos-page-content

licence.php:
- <div class="apropos-description apropos-page-content apropos-single"> →
  <div class="prose apropos-single"> (consistent with apropos.php rename)

apropos.css:
- Rename .apropos-description / .apropos-page-content → .prose; merge all prose
  content rules under the single .prose selector
- Rename .apropos-right → .apropos-aside; remove .apropos-left (empty rule)
- Replace .apropos-contact, .apropos-contact-name etc. with element selectors:
  .apropos-aside address, .apropos-aside address strong,
  .apropos-aside address span, .apropos-aside address a
- Update responsive blocks to reference .prose instead of .apropos-description

public/licence.php

@@ -39,7 +39,7 @@ $extraCss = ['assets/apropos.css'];
     <?php include APP_ROOT . '/templates/search-bar.php'; ?>
 
     <main class="apropos-main" id="main-content">
-        <div class="apropos-description apropos-page-content apropos-single">
+        <div class="prose apropos-single">
             <?php if (!empty(trim($content))): ?>
                 <?= $html ?>
             <?php else: ?>