fix(e2e): stabilize report branding cross-browser

[luandro]

Closes #359

Summary

• replace WebKit-hostile context-level offline mode with deterministic request blocking for the local-only report-branding flow
• block service-worker control in that offline test so Playwright can enforce the network boundary
• wait for domcontentloaded instead of unrelated full-load completion before locator-driven assertions
• add report-branding to the Firefox/WebKit PR E2E subset and guard that CI contract with a unit test
• add reproducible QA at docs/qa/359.md plus scripts/qa/359-report-branding-e2e.sh

Validation

• npm run lint ✅
• targeted ReportBrandingDialog + guardrail tests: 23/23 ✅
• npm run lint:types ✅
• npm run check:i18n ✅
• npm run build:ci ✅
• Chromium + Firefox report-branding E2E, retries disabled: 4/4 ✅
• WebKit representative PR ordering, retries disabled: 5/5 ✅
• WebKit previously failing offline case repeated 3×, retries disabled: 3/3 ✅
• full local npm run test:coverage exceeded the 180s connector execution ceiling while still progressing through passing suites; exact-SHA GitHub CI is the authoritative coverage gate

QA

QA #359 — report-branding cross-browser CI recovery

[github-actions]

React Doctor found no new issues. 🎉

_{Reviewed by React Doctor for commit ed06b79.}

[github-actions]

Preview deployment ready: https://fix-359-report-branding-e2e.comapeo-cloud-app.pages.dev

Commit: faa1e16