Accounts and sign-in, and fix the read toggle

epAction's redraw closure called itself when handed a row, so Mark read
recursed until the stack blew; it now swaps that row in place. Opening an
item also marks it read, redrawn where it stands so nothing vanishes from
under the pointer on the Unread tab.

Step A of multi-user: users and sessions tables, Argon2id, a session
cookie, ipx user subcommands, and a trusted proxy header for Cloudflare
Zero Trust -- honoured only from a trusted_proxies address. The shared
token still works and is the admin. A new database starts with
admin/ipodderx.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AdXho5tTkjFLeUXKbEjKBh

tests/ui/app.spec.js

@@ -234,3 +234,25 @@ test.describe('on a phone', () => {
     await expect(page.locator('#detail')).not.toBeVisible();
   });
 });
+
+test('opening an item marks it read, and the toggle flips it back', async ({ page }) => {
+  const errors = [];
+  page.on('pageerror', e => errors.push(e.message));
+
+  await page.getByText('Test Show').click();
+  const row = () => page.locator('.ep', { hasText: 'Second Episode' });
+  await expect(row()).toBeVisible({ timeout: 20_000 });
+
+  // Another test may have opened this item already, so start from a known state: the
+  // toggle in the text below flips it back -- which used to recurse until the stack blew.
+  await row().click();
+  await page.locator('#detail button', { hasText: 'Mark unread' }).click();
+  await expect(row()).not.toHaveClass(/read/);
+  await expect(page.locator('#detail button', { hasText: 'Mark read' })).toBeVisible();
+
+  // Opening it is reading it.
+  await row().click();
+  await expect(row()).toHaveClass(/read/);
+
+  expect(errors).toEqual([]);
+});