Add a read-only role per app for calendar, feedback and tickets

A grant can now be `read` instead of `access`: requireAppAccess lets it
through for GET/HEAD/OPTIONS and answers 403 to every other method, so
new write routes are covered without being marked. `read` and `access`
on the same app are rejected together; user management has no read role.
/tickets/admin/me and /feedback/admin/me report `readOnly`.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

test/admin/admin.schema.test.ts

@@ -1,9 +1,12 @@
 import {describe, expect, it} from 'vitest';
 import {
 	ACCESS_ROLE,
+	READ_ROLE,
 	appsOf,
+	canWrite,
 	isAppPermission,
 	isAppRole,
+	isReadOnly,
 	toPermissions
 } from '../../src/models/admin/admin.schema.js';
 
@@ -59,6 +62,44 @@ describe('toPermissions', () => {
 	it('reads an empty list as "no permissions", not as invalid', () => {
 		expect(toPermissions([])).toEqual([]);
 	});
+	it('reads the read-only role', () => {
+		expect(toPermissions([{app: 'tickets', role: READ_ROLE}])).toEqual([
+			{app: 'tickets', role: READ_ROLE}
+		]);
+	});
+
+	it('rejects full and read-only access to the same app together', () => {
+		expect(toPermissions(['tickets', {app: 'tickets', role: READ_ROLE}])).toBeNull();
+	});
+
+	it('allows full access to one app next to read-only access to another', () => {
+		expect(toPermissions(['tickets', {app: 'feedback', role: READ_ROLE}])).toEqual([
+			{app: 'tickets', role: ACCESS_ROLE},
+			{app: 'feedback', role: READ_ROLE}
+		]);
+	});
+
+	it('rejects read-only access to user management', () => {
+		expect(toPermissions([{app: 'admin', role: READ_ROLE}])).toBeNull();
+	});
+});
+
+describe('canWrite / isReadOnly', () => {
+	it('lets only the access role write', () => {
+		const permissions = [
+			{app: 'tickets' as const, role: ACCESS_ROLE},
+			{app: 'feedback' as const, role: READ_ROLE}
+		];
+		expect(canWrite(permissions, 'tickets')).toBe(true);
+		expect(canWrite(permissions, 'feedback')).toBe(false);
+		expect(isReadOnly(permissions, 'tickets')).toBe(false);
+		expect(isReadOnly(permissions, 'feedback')).toBe(true);
+	});
+
+	it('is neither for an app without any grant', () => {
+		expect(canWrite([], 'calendar')).toBe(false);
+		expect(isReadOnly([], 'calendar')).toBe(false);
+	});
 });
 
 describe('isAppRole', () => {