feat(db): pack_files 테이블 마이그레이션 — Phase 2 자료 다운로드 SSOT

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

supabase/migrations/2026-05-02-create-pack-files.sql

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+-- Phase 2: pack_files 테이블 — Music 팩 자료 메타데이터 SSOT
+
+create table public.pack_files (
+  id uuid primary key default gen_random_uuid(),
+  min_tier text not null check (min_tier in ('starter', 'pro', 'master')),
+  label text not null,
+  file_path text not null unique,
+  filename text not null,
+  size_bytes bigint not null,
+  sort_order int not null default 0,
+  uploaded_at timestamptz not null default now(),
+  deleted_at timestamptz
+);
+
+create index idx_pack_files_tier on public.pack_files(min_tier, sort_order)
+  where deleted_at is null;
+
+alter table public.pack_files enable row level security;
+
+-- 일반 사용자 직접 SELECT 차단. /api/packs/* 라우트가 service role로 조회.
+-- (RLS enabled + 정책 미정의 → 모든 anon/authenticated SELECT 거부)