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

db/migration.sql

@@ -223,3 +223,13 @@ ON CONFLICT (key) DO NOTHING;
 
 ALTER TABLE entries ADD COLUMN IF NOT EXISTS photo_original_path VARCHAR(255);
 ALTER TABLE photo_jobs ADD COLUMN IF NOT EXISTS applied BOOLEAN NOT NULL DEFAULT false;
+
+CREATE TABLE IF NOT EXISTS modules (
+  id SERIAL PRIMARY KEY,
+  name VARCHAR(200) NOT NULL UNIQUE,
+  lessons_count INT NOT NULL DEFAULT 0,
+  created_at TIMESTAMPTZ DEFAULT now()
+);
+
+ALTER TABLE entries ADD COLUMN IF NOT EXISTS module_id INT REFERENCES modules(id) ON DELETE SET NULL;
+CREATE INDEX IF NOT EXISTS idx_entries_module_id ON entries(module_id);