feat: customer relationship view, idempotency keys, approval decline, seed payments, backlog cleanup

- #3: Wire ApprovalModal handleDecline to POST /api/admin/bookings/{id}/cancel
- #25: New GET /api/admin/users/{id}/relationship endpoint with spend, tips, visits, customer-for duration, top services
- #25: UserModal reorganized — Personal Info, Booking History, Customer Relationship, Loyalty, Patch Tests
- #36: Idempotency keys on user and admin booking creation (UUID header, duplicate detection)
- local-dev-2.sh: seed payments via PL/pgSQL for completed bookings (5 randomized scenarios)
- local-dev-2.sh: shrink guest/time-blocker output, add payments to summary
- Backlog: mark #3/#25/#35/#36/#49 done, plan #36/#45, remove #46/#48, update #45 with milestone campaigns
- Remove notes history table, avg visits/year metric, Account Information, Privacy & Consent from UserModal

init-scripts/init-script.sql

@@ -216,7 +216,8 @@ CREATE TABLE bookings (
     deposit_required BOOLEAN NOT NULL DEFAULT FALSE,
     created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
     updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
-    created_by CHAR(12)
+    created_by CHAR(12),
+    idempotency_key VARCHAR(64) UNIQUE
 );
 
 CREATE INDEX idx_bookings_userid ON bookings(user_id);