Testing Maple's web app on PR previews with e2e

Browser tests against a deployed Maple stack, written with e2e. They catch what unit and component tests can't: a rule made by the API and edited in the UI, a preview query that only fails on the deployed warehouse.

Run against a PR preview (signs in as the shared preview reviewer, see docs/pr-previews.md):

cd apps/web/e2e
E2E_TELEMETRY_DISABLED=1 MAPLE_E2E_APP_URL=https://app-pr-<n>.maple.dev \
  infisical run --env dev -- bunx e2e run

• tests/auth.setup.e2e.ts trades PREVIEW_SIGNIN_KEY for a single-use Clerk ticket in the runner, so the key never reaches the page, a trace, or a model.
• tests/support.ts api() calls the v2 API from the page with its Clerk session, for setup and for asserting what was saved.
• Assert with locators and expect. No model is configured, so agent.* steps are unavailable.
• Tests create their own rules and destinations with a run-unique suffix and delete them after.

CI runs this as the e2e job of deploy-pr-preview.yml, after the preview's seed and smoke test. It is not a required check, and it reruns without redeploying. Traces and screenshots land in the e2e-results artifact.