feat(dimentorin): materials module (CRUD konten mentoring, public+protected routes)

- app_materials table: mentor_id, title, slug, category, description, content
- domain/application/infrastructure pola articles: repo postgres, service, DTO ZodValidate
- routes: GET /materials (public, published only), GET /materials/{id|slug|categories}, POST/PUT/DELETE (auth, author-only)
- verified e2e: create 3 materi sebagai mentor, list, slug, categories

imphnen-dimentorin/src/materials/infrastructure/persistence/mod.rs

@@ -0,0 +1,3 @@
+pub mod postgres_material_repository;
+
+pub use postgres_material_repository::PostgresMaterialRepository;