feat: implement structured grading system with predefined assessment types

- Add structured grading policy with predefined types (Continuous Assessment, Midterm, Final Test, Exam)
- Replace free-text category input with combobox selection in Grading Policy page
- Update Lesson Editor to use dropdown selector for grading category assignment
- Fix create_grading_category handler to capture organization context
- Fix update_course handler to set audit context in database transaction
- Implement getImageUrl helper for proper asset path resolution
- Add unoptimized prop to organization logo images to bypass Next.js optimization
- Add database migrations for organization_id in content tables
- Seed default tutorial courses for Admin, Instructor, and Student roles
- Fix audit log constraints and content schema issues

web/studio/src/lib/api.ts

@@ -1,5 +1,15 @@
 export const API_BASE_URL = process.env.NEXT_PUBLIC_CMS_API_URL || "http://localhost:3001";
 
+export const getImageUrl = (path?: string) => {
+    if (!path) return '';
+    if (path.startsWith('http')) return path;
+    // Map /uploads to /assets if backend stores relative paths
+    // The main.rs serves "uploads" dir at "/assets" route
+    const cleanPath = path.startsWith('/uploads') ? path.replace('/uploads', '/assets') : path;
+    const finalPath = cleanPath.startsWith('/') ? cleanPath : `/${cleanPath}`;
+    return `${API_BASE_URL}${finalPath}`;
+};
+
 export interface Course {
     id: string;
     title: string;