fix: clean rebuild — all 13 section IDs + TOC order + About stays last

- Restored from 8db9f44 (clean base)
- Added IDs to all subsections via unique HTML context
- TOC reordered: Search, Recent, Backend, Tags, Sync, Hidden, Webhooks, Shares, Diags, AI, Themes, Profile, About
- About section at original position (last), no moved sections

frontend/index.html

@@ -2032,7 +2032,10 @@
                             </section>
 
                             <!-- À propos -->
-                            
+                            <section
+                                class="config-section help-section"
+                                id="cfg-about"
+                            >
                                 <h2 data-i18n="auto.a3319169">📦 À propos</h2>
                                 <div
                                     id="config-about"
@@ -2075,11 +2078,8 @@
                             </section>
 
                             <!-- Partages publics -->
-                            <section class="config-section help-section"><section
-                                class="config-section help-section"
-                                id="cfg-about"
-                            >
-                                <h2 id="cfg-partages-publics">📤 Partages publics</h2>
+                            <section id="cfg-partages-publics" class="config-section help-section">
+                                <h2>📤 Partages publics</h2>
                                 <p class="config-description">
                                     Liens de partage publics pour des documents
                                     (lecture seule, sans authentification).