scan-alert-hardening: different-finder re-alert within 250m window + fingerprint 24h block (12/12 scenarios pass)

db/schema.sql

@@ -63,3 +63,6 @@ CREATE TABLE IF NOT EXISTS orders (
 -- Tag → product / order linkage (populated by the Laravel admin, Phase 4).
 ALTER TABLE tags ADD COLUMN IF NOT EXISTS product_id BIGINT REFERENCES products(id);
 ALTER TABLE tags ADD COLUMN IF NOT EXISTS order_id BIGINT REFERENCES orders(id);
+
+-- Phase 2.5: per-device anti-spam fingerprint on scans (idempotent).
+ALTER TABLE scans ADD COLUMN IF NOT EXISTS fingerprint TEXT;