feat: migrate app state to bootstrap endpoint

Use GET /me/bootstrap as the primary authenticated state source per ADR-0003. AuthContext now fetches and exposes typed bootstrapData, Header and class/detail admin checks use bootstrap permissions/roles, dashboard surfaces onboarding/calendar/timetable/graph status, and graph navigation derives school setup state from bootstrap instead of /school/status.

Refs: t_44353587

src/pages/Header.tsx

@@ -1,4 +1,4 @@
-import React, { useEffect, useState, useCallback } from 'react';
+import React, { useEffect, useState } from 'react';
 import { useNavigate, useLocation } from 'react-router-dom';
 import { useAuth } from '../contexts/AuthContext';
 import {
@@ -38,54 +38,24 @@ import { HEADER_HEIGHT } from './Layout';
 import { logger } from '../debugConfig';
 import { GraphNavigator } from '../components/navigation/GraphNavigator';
 
-const API_BASE = import.meta.env.VITE_API_URL || 'http://localhost:8000';
 
 const Header: React.FC = () => {
   const theme = useTheme();
   const navigate = useNavigate();
   const location = useLocation();
-  const { user, signOut, accessToken } = useAuth();
+  const { user, signOut, bootstrapData } = useAuth();
   const [anchorEl, setAnchorEl] = useState<null | HTMLElement>(null);
-  const [isPlatformAdmin, setIsPlatformAdmin] = useState(false);
-  const [schoolRole, setSchoolRole] = useState<string | null>(null);
   const [isAuthenticated, setIsAuthenticated] = useState(!!user);
   const showGraphNavigation = location.pathname === '/single-player';
+  const isPlatformAdmin = bootstrapData?.permissions?.platform_admin ?? false;
+  const schoolRole = bootstrapData?.active_institute?.membership_role ?? null;
   const isSchoolAdmin = schoolRole === 'school_admin' || schoolRole === 'department_head';
 
   useEffect(() => {
     setIsAuthenticated(!!user);
   }, [user]);
 
-  // Check platform admin status and school role once on login
-  const checkAdminStatus = useCallback(async () => {
-    if (!accessToken) return;
-    // Platform admin check
-    try {
-      const res = await fetch(`${API_BASE}/admin/stats`, {
-        headers: { Authorization: `Bearer ${accessToken}` },
-      });
-      setIsPlatformAdmin(res.ok);
-    } catch {
-      setIsPlatformAdmin(false);
-    }
-    // School role check
-    try {
-      const res = await fetch(`${API_BASE}/school/status`, {
-        headers: { Authorization: `Bearer ${accessToken}` },
-      });
-      if (res.ok) {
-        const data = await res.json();
-        setSchoolRole(data.user_role || null);
-      }
-    } catch {
-      setSchoolRole(null);
-    }
-  }, [accessToken]);
 
-  useEffect(() => {
-    if (accessToken) checkAdminStatus();
-    else { setIsPlatformAdmin(false); setSchoolRole(null); }
-  }, [accessToken, checkAdminStatus]);
 
   const handleMenuOpen = (event: React.MouseEvent<HTMLElement>) => {
     setAnchorEl(event.currentTarget);