fix: fetch script sources for V8 coverage on network-loaded scripts

The @bgotink/playwright-coverage library's mixinCoverage fixture relies on
script.source being present in V8 coverage data, but Playwright only includes
source for inline scripts, not network-loaded ones. Since Vite bundles are
served over HTTP, all coverage entries had null sources, resulting in 0/0
coverage.

Replace mixinCoverage with a custom page fixture that:
1. Starts/stops V8 JS coverage as before
2. After stopping, fetches the source text for any network-loaded script
   that is missing its source
3. Writes the enriched coverage data as an attachment for the reporter

browser_tests/fixtures/ComfyPage.ts

@@ -1,7 +1,7 @@
 import type { APIRequestContext, Locator, Page } from '@playwright/test'
 import { test as base } from '@playwright/test'
-import { mixinFixtures as mixinCoverage } from '@bgotink/playwright-coverage'
 import { config as dotenvConfig } from 'dotenv'
+import { promises as fs } from 'fs'
 
 import { NodeBadgeMode } from '../../src/types/nodeSource'
 import { ComfyActionbar } from '@e2e/helpers/actionbar'
@@ -401,12 +401,43 @@ export class ComfyPage {
 
 export const testComfySnapToGridGridSize = 50
 
-const baseWithCoverage = mixinCoverage(base)
+const COLLECT_COVERAGE = process.env.COLLECT_COVERAGE === 'true'
+const COVERAGE_ATTACHMENT = '@bgotink/playwright-coverage'
 
-export const comfyPageFixture = baseWithCoverage.extend<{
+export const comfyPageFixture = base.extend<{
   comfyPage: ComfyPage
   comfyMouse: ComfyMouse
+  collectCoverage: boolean
 }>({
+  collectCoverage: [COLLECT_COVERAGE, { option: true }],
+
+  page: async ({ page, collectCoverage, browserName }, use, testInfo) => {
+    if (browserName !== 'chromium' || !collectCoverage) {
+      return use(page)
+    }
+
+    await page.coverage.startJSCoverage({ resetOnNavigation: false })
+    await use(page)
+    const entries = await page.coverage.stopJSCoverage()
+
+    for (const entry of entries) {
+      if (typeof entry.source !== 'string' && entry.url.startsWith('http')) {
+        try {
+          const resp = await fetch(entry.url)
+          if (resp.ok) (entry as Record<string, unknown>).source = await resp.text()
+        } catch {}
+      }
+    }
+
+    const resultFile = testInfo.outputPath('v8-coverage.json')
+    await fs.writeFile(resultFile, JSON.stringify({ result: entries }))
+    testInfo.attachments.push({
+      name: COVERAGE_ATTACHMENT,
+      contentType: 'application/json',
+      path: resultFile
+    })
+  },
+
   comfyPage: async ({ page, request }, use, testInfo) => {
     const comfyPage = new ComfyPage(page, request)