Add Todo module: SPA task manager with lists, priorities and due dates

- New todo.php SPA page with sidebar (smart views + user lists)
- modules/todo/api.php: REST API for lists and todos (CRUD, filters, stats)
- modules/todo/assets/todo.js: frontend (quick add, toggle done, modals)
- modules/todo/assets/todo.css: full light/dark theme styles
- pf_todo_lists + pf_todos tables added to schema_family.sql
- Integrated in header nav, home page cards, settings module list
- Translations added in fr/en/ca

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

index.php

@@ -100,6 +100,15 @@ if ($_has_custom_bg): ?>
       </a>
       <?php endif; ?>
 
+      <?php if (in_array('todo', $mods)): ?>
+      <a href="/todo.php" class="pf-module-card">
+        <div class="pf-card-icon">✅</div>
+        <h3 class="pf-card-title"><?= tr('mod_todo_name') ?></h3>
+        <div class="pf-card-desc"><?= tr('mod_todo_desc') ?></div>
+        <span class="pf-card-cta"><?= tr('cta_open') ?></span>
+      </a>
+      <?php endif; ?>
+
     </div>
   </section>
 </div>