feat(phase2): 일일 사용량 유틸(KST) + tarot_readings·ai_usage_log 마이그레이션

- kstDayStartISO: KST 자정을 UTC ISO로 변환
- getTodayUsage, recordUsage: AI 사용량 조회·기록
- DB: tarot_readings, ai_usage_log 테이블 생성
- saju service_settings 삭제 (숨김 해제)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AAtcmKKtqDUe4NyVgy1aLQ

supabase/migrations/2026-07-02-phase2-saju-tarot.sql

@@ -0,0 +1,27 @@
+-- Phase 2 (2026-07-02): 타로 저장·AI 사용량 로그 + 사주 숨김 해제
+-- 적용: 클라우드 Supabase + NAS self-host 양쪽
+
+CREATE TABLE IF NOT EXISTS tarot_readings (
+  id uuid PRIMARY KEY DEFAULT gen_random_uuid(),
+  user_id uuid NOT NULL REFERENCES auth.users(id) ON DELETE CASCADE,
+  spread_type text NOT NULL DEFAULT 'three_card',
+  category text,
+  question text,
+  cards jsonb NOT NULL,
+  interpretation jsonb NOT NULL,
+  summary text,
+  created_at timestamptz NOT NULL DEFAULT now()
+);
+ALTER TABLE tarot_readings ENABLE ROW LEVEL SECURITY;
+CREATE POLICY tarot_select_own ON tarot_readings FOR SELECT USING (auth.uid() = user_id);
+
+CREATE TABLE IF NOT EXISTS ai_usage_log (
+  id uuid PRIMARY KEY DEFAULT gen_random_uuid(),
+  user_id uuid NOT NULL,
+  service text NOT NULL CHECK (service IN ('saju','tarot')),
+  created_at timestamptz NOT NULL DEFAULT now()
+);
+ALTER TABLE ai_usage_log ENABLE ROW LEVEL SECURITY;
+CREATE INDEX IF NOT EXISTS idx_ai_usage_user_day ON ai_usage_log (user_id, service, created_at);
+
+DELETE FROM service_settings WHERE id = 'saju';