test(e2e): add Playwright test for avatar cache invalidation

Uploads two different avatars in sequence and verifies the header
avatar src changes after the second upload. This confirms both the
backend cache (via DelPrefix) and the frontend cache are properly
invalidated when a new avatar is uploaded.

frontend/tests/e2e/user/settings.spec.ts

@@ -40,6 +40,54 @@ test.describe('User Settings', () => {
 		await expect(page.locator('.global-notification')).toContainText('Success', {timeout: 10000})
 	})
 
+	test('Invalidates avatar cache when uploading a new avatar', async ({authenticatedPage: page}) => {
+		await page.goto('/user/settings/avatar')
+		await page.waitForLoadState('networkidle')
+
+		const uploadRadio = page.locator('input[name=avatarProvider][value=upload]')
+		await expect(uploadRadio).toBeVisible({timeout: 5000})
+		await uploadRadio.click()
+
+		const fileInput = page.locator('input[type=file]')
+		const uploadButton = page.locator('[data-cy="uploadAvatar"]')
+		const headerAvatar = page.locator('.username-dropdown-trigger img.avatar')
+		const notification = page.locator('.global-notification')
+
+		// Upload first avatar (image.jpg)
+		await fileInput.setInputFiles('tests/fixtures/image.jpg')
+		await expect(uploadButton).toBeEnabled({timeout: 10000})
+
+		const firstUploadPromise = page.waitForResponse(response =>
+			response.url().includes('avatar') && response.request().method() === 'PUT',
+		)
+		await uploadButton.click()
+		const firstResponse = await firstUploadPromise
+		expect(firstResponse.ok()).toBe(true)
+		await expect(notification).toContainText('Success', {timeout: 10000})
+
+		// Wait for the header avatar to update and capture its src
+		await expect(headerAvatar).toHaveAttribute('src', /blob:|data:/, {timeout: 10000})
+		const firstAvatarSrc = await headerAvatar.getAttribute('src')
+
+		// Wait for the notification to disappear before uploading again
+		await expect(notification).not.toBeVisible({timeout: 10000})
+
+		// Upload second avatar (image-blue.png)
+		await fileInput.setInputFiles('tests/fixtures/image-blue.png')
+		await expect(uploadButton).toBeEnabled({timeout: 10000})
+
+		const secondUploadPromise = page.waitForResponse(response =>
+			response.url().includes('avatar') && response.request().method() === 'PUT',
+		)
+		await uploadButton.click()
+		const secondResponse = await secondUploadPromise
+		expect(secondResponse.ok()).toBe(true)
+		await expect(notification).toContainText('Success', {timeout: 10000})
+
+		// Verify the header avatar changed to a different blob URL
+		await expect(headerAvatar).not.toHaveAttribute('src', firstAvatarSrc!, {timeout: 10000})
+	})
+
 	test('Updates the name', async ({authenticatedPage: page}) => {
 		await page.goto('/user/settings/general')
 		await page.waitForLoadState('networkidle')