e2e: schedule viewing spec (timeline + list, reveal levels)

This was generated by AI during triage.

Slice of the e2e coverage epic #106, following the pattern proven by #111 (voting spec, PR #150).

Goal

Playwright e2e spec for schedule/sets viewing across reveal levels, against the local-Supabase harness.

At reveal level full: timeline and list views show seeded sets under the correct day/stage with times.
Switching between timeline and list views works and preserves the selected day.
At a lower reveal level (e.g. days): times/stages are masked appropriately and the placeholder/masked UI renders (see src/lib/scheduleReveal.ts and ADR 0001).
At draft: the schedule shows the not-revealed placeholder rather than sets.
Navigating from a schedule entry to the set detail page works.

Build on the existing Playwright setup and TestHelpers; semantic selectors, minimal data-testid additions only where needed.
Seed must provide an edition with timed sets on known days/stages, and a way to exercise different reveal levels (either seed multiple editions at different levels, or set the level via seeded admin state). Extend supabase/seed.sql as needed — no production-synced data.

pnpm run test:setup then pnpm run test:e2e green locally; deterministic across repeated runs.

Voting (#111), groups, admin, set-detail — separate slices under #106.