e2e: admin dashboard spec (artist/set management, permissions)

[chiptus]

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 the admin surface, against the local-Supabase harness.

Behaviors to cover

• A core-team user can reach the admin dashboard; a regular user cannot (redirect or denial — assert the negative).
• Admin can create an artist and it appears in the artists table and public views.
• Admin can edit an artist/set (e.g. rename, change stage/time) and the change is reflected.
• Admin sets table renders sets without times with the "—" placeholder (existing behavior).
• Archive/delete flow if present: archived item disappears from public views.

Harness & preconditions

• Build on existing Playwright setup and TestHelpers; minimal data-testid additions only where needed.
• Seed must provide a core-team/admin test user and a regular user; extend supabase/seed.sql if missing — no production-synced data.

Verification

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

Out of scope

Voting (#111), groups, schedule/reveal, set-detail — separate slices under #106. Schedule import (Analyse/Commit) flows are their own future surface.