Port the vesting e2e Playwright suite

[gabitoesmiapodo]

User story / Problem statement

The vesting app has no browser-level tests. The source repo carries a Playwright suite at dapp/e2e that was not imported, and this repo has no Playwright anywhere.

Expected outcome

The critical vesting flows are covered end-to-end in a browser: green against mock mode today, and against the live stack once it exists.

Acceptance criteria

• Playwright added to the workspace with its bundled Chromium
• Suite ported from cn-dappbooster@feat/vesting-lite dapp/e2e, source commit recorded
• Mock-mode run is green with zero services and gated in .github/workflows/pr.yml
• Live-stack run documented, enabled once the live-ledger wiring lands
• pnpm-workspace.yaml allowBuilds updated if the install requires it

Technical notes

Mock mode needs no services, so the suite's mock half can land immediately and gate CI on its own. Only the live-stack half depends on the live-ledger wiring; land that as a second PR. Deliberately left unblocked for this reason.

Additional context

Follow-up 4 from PR #35.