fix: enforce gallery access and consolidate gallery workflows (#1357)

Harden gallery authentication and authorization, consolidate gallery workflows, and prevent token-bearing URLs from leaking through nginx request error logs.

backend/__tests__/services/scheduledTask.test.js

@@ -0,0 +1,25 @@
+jest.mock('../../src/utils/logger', () => ({ error: jest.fn() }));
+const { scheduledTask } = require('../../src/services/scheduledTask');
+beforeEach(() => jest.useFakeTimers());
+afterEach(() => jest.useRealTimers());
+it('starts once, skips overlap and drains the accepted run on stop', async () => {
+  let finish;
+  const work = jest.fn(() => new Promise(resolve => { finish = resolve; }));
+  const task = scheduledTask(work, { interval: 100 });
+  task.start(); task.start();
+  expect(jest.getTimerCount()).toBe(1);
+  await jest.advanceTimersByTimeAsync(300);
+  expect(work).toHaveBeenCalledTimes(1);
+  let stopped = false;
+  const stop = task.stop().then(() => { stopped = true; });
+  await Promise.resolve(); expect(stopped).toBe(false);
+  finish(); await stop; expect(stopped).toBe(true);
+  expect(jest.getTimerCount()).toBe(0);
+  await jest.advanceTimersByTimeAsync(1000); expect(work).toHaveBeenCalledTimes(1);
+});
+it('cancels a delayed first run and can restart cleanly', async () => {
+  const work = jest.fn(); const task = scheduledTask(work, { interval: 100, initialDelay: 10 });
+  task.start(); await task.stop(); await jest.advanceTimersByTimeAsync(200); expect(work).not.toHaveBeenCalled();
+  task.start(); await jest.advanceTimersByTimeAsync(10); expect(work).toHaveBeenCalledTimes(1);
+  await task.stop();
+});