i18n: About page fully internationalized

HTML:
- tagline: data-i18n-html for line break support
- stats labels: about.files instead of palette.mode_files
- built_with, last_delivery, made_with: data-i18n spans

config.js:
- Months array: 12 French months -> t('month.*')
- Jokes array: 10 French jokes -> t('about.joke_*')
- Joke display: removed hardcoded «» wrappers

Locales:
- +34 new keys (months, jokes, about labels)
- 1231 keys in each locale

frontend/index.html

@@ -375,7 +375,7 @@
                                 id="search-dropdown-titles"
                             >
                                 <div class="search-dropdown__section-header">
-                                    <span data-i18n="palette.mode_files">Fichiers</span>
+                                    <span data-i18n="about.files">Files</span>
                                 </div>
                                 <ul
                                     class="search-dropdown__list"
@@ -4792,7 +4792,7 @@ curl -X POST https://votre-serveur.com/webhook \
                         </svg>
                     </div>
                     <h1 class="about-title" data-i18n="header.logo">ObsiGate</h1>
-                    <p class="about-tagline">Vos notes Obsidian,<br>simplement accessibles.</p>
+                    <p class="about-tagline" data-i18n-html="about.tagline">Vos notes Obsidian,<br>simplement accessibles.</p>
                     <span class="about-version">v2.0.0-dev</span>
                 </div>
                 <div class="about-body">
@@ -4833,7 +4833,7 @@ curl -X POST https://votre-serveur.com/webhook \
                             <span>Git&nbsp;: <strong id="about-commit">—</strong></span>
                         </div>
                         <p class="about-joke" id="about-joke"></p>
-                        <p class="about-copy">&copy; 2026 — Fait avec ☕, 🎧 et quelques <code>git push --force</code> accidentels.</p>
+                        <p class="about-copy">&copy; 2026 — <span data-i18n="about.made_with">Fait avec ☕, 🎧 et quelques <code>git push --force</code> accidentels.</span></p>
                     </div>
                 </div>
             </div>