feat(brand): unify on Deck Hearth across in-repo strings + infra (P1 brand decision)
Resolves the launch-blocking 'TCG Vault vs Deck Hearth' inconsistency called out in AGENTS.md line 5 since project setup. Operator gate-0 decision: Deck Hearth wins. Two briefs applied serially. B1 (mechanical): 7-file display + comment sweep. B2 (infrastructure): Redis prefix rename in lib/rate-limit.js (5 prefixes, accept one-time counter reset), package.json + lockfile regen (STOP-on-churn confirmed only name lines changed), admin/alice/bob email rename in seed scripts + login pre-fill + NEW idempotent migration script scripts/migrations/2026-05-24-rename-admin-email.js. Risk 4 PRESERVE applied: test/lib/permission-middleware.test.js retains admin@tcgvault.com literal with 7-line architect-authored why comment (documents pre-fix-auth-bypass bug shape; preserves historical truth per project's gotcha-documentation convention). All 5 D-decisions ratified at gate-1 (Deck Hearth / deck-hearth / deckhearth / admin@deckhearth.com / full deckhearth Redis prefix). Local: lint 128 baseline (B1 + B2), vitest 21/21 (B1 + B2). CI all green: Playwright smoke 3/3 against rebranded preview in 1m4s, forbidden-cors-headers pass, forbidden-endpoints pass, Screenshot diff pass, Vercel deployment complete. Cross-validation lineage: 4th convoy where the same 3-test smoke spec defends auth surface through sweeping change (after PR #15 Layout default-user, PR #19 CORS, PR #20 rate-limit, now this PR #21 brand rename). OPERATOR POST-MERGE ACTION REQUIRED: run 'node scripts/migrations/2026-05-24-rename-admin-email.js' against prod Neon DB before next admin login (ordering: migration FIRST, then any subsequent setup-db invocation). Migration is ESM, idempotent, UNIQUE-collision-safe. PR #21 architect-commit 50ce9ab, B1 ac8c998, B2 1c18d21.
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