refactor: extract mergePullRequestViaUI helper to pages/sessions

[empiricalrun]

Summary

Extracted the repeated PR merge UI flow into a single mergePullRequestViaUI helper in tests/pages/sessions.ts.

Problem

The following 4-step sequence was copy-pasted verbatim across 4 spec files:

await page.getByRole('button', { name: 'Review' }).click();
await page.getByRole('button', { name: 'Merge PR' }).click();
await page.getByRole('button', { name: 'Merge PR' }).click(); // confirmation
await page.waitForTimeout(3000);

Files affected

File	Change
tests/pages/sessions.ts	➕ New mergePullRequestViaUI(page) helper
tests/merge-conflicts.spec.ts	✅ Uses new helper
tests/merge-conflicts-impacted-tests.spec.ts	✅ Uses new helper
tests/edit-message-branch-restore.spec.ts	✅ Uses new helper
tests/session-two-prs.spec.ts	✅ Uses new helper

Verification

• grep "Merge PR" tests/**/*.spec.ts → 0 matches (no duplicate sequences remain)
• tsc --noEmit → no errors

PR created from session #111898

^{Updated at 2026-04-06 04:54:15.145 UTC}