feat: route permission guards, home page per role — RolePermissionsContext, PermissionGuard, App routes, DB migration

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/migrations/081_role_permissions_home_page.sql

@@ -0,0 +1,2 @@
+ALTER TABLE role_permissions
+  ADD COLUMN IF NOT EXISTS home_page VARCHAR(100) DEFAULT NULL;