Gradebook: classes, weighted grading, assignments, grades, student role

- Migration: student role, students.user_id, grade_categories/grade_scale
  (school defaults + per-class override), assignments, grades + RLS
- Classes area (nav): list/create classes, class page with Gradebook / Roster /
  Grading setup tabs; teachers see their classes, admins all
- Weighted-category grade calc -> letter scale (shared helper)
- Roster assignment (admin), assignment + grade entry (teacher/admin)
- Student profile: view-only Grades tab (parents/students)
- Portal access: create parent OR student logins linked to the student

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/hooks/use-auth.ts

@@ -2,7 +2,7 @@ import { useEffect, useState } from "react";
 import type { User } from "@supabase/supabase-js";
 import { supabase } from "@/integrations/supabase/client";
 
-export type Role = "admin" | "teacher" | "parent";
+export type Role = "admin" | "teacher" | "parent" | "student";
 
 export interface AuthState {
   user: User | null;
@@ -52,5 +52,6 @@ export function highestRole(roles: Role[]): Role | null {
   if (roles.includes("admin")) return "admin";
   if (roles.includes("teacher")) return "teacher";
   if (roles.includes("parent")) return "parent";
+  if (roles.includes("student")) return "student";
   return null;
 }