feat(modules): module topics for student form, admin CRUD with pagination

- db: modules table (name, lessons_count) + entries.module_id (ON DELETE SET NULL), migration + idempotent startup ensure
- api: GET /api/modules (public, search + limit/offset, entries_count), POST/PUT/DELETE (admin, audit-logged)
- entries: accept/validate module_id on create/update, return module_name, module_id filter
- backup/restore: include modules and entries.module_id
- student form: required module select, hidden while no modules exist
- admin: modules.html + js/modules.js list with pagination, search, create/edit/delete modal
- journal: module filter, module select in edit modal, module badge, CSV column

public/index.html

@@ -127,6 +127,13 @@ nav a:hover{color:var(--text)}
       </select>
     </div>
 
+    <div class="field" id="moduleField" style="display:none">
+      <label>Тема модуля</label>
+      <select id="moduleInput">
+        <option value="">— выбери тему —</option>
+      </select>
+    </div>
+
     <div class="field">
       <label>Что сделал</label>
       <textarea id="descInput" placeholder="Опиши, что проходил, что делал на занятии..." required></textarea>