Add shipping cost groups and reject spam contact-form SMS.

Wire cart/checkout shipping fees with category groups and static rates, reject gibberish contact submissions, and SMS only valid Iranian mobiles.

Co-authored-by: Cursor <cursoragent@cursor.com>

database/migrations/101_shipping_cost_group_is_default.sql

@@ -0,0 +1,8 @@
+-- Default shipping cost group per business (fallback for unassigned categories)
+
+ALTER TABLE shipping_cost_groups
+  ADD COLUMN IF NOT EXISTS is_default BOOLEAN NOT NULL DEFAULT FALSE;
+
+CREATE UNIQUE INDEX IF NOT EXISTS uq_shipping_cost_groups_business_default
+  ON shipping_cost_groups (business_id)
+  WHERE is_default = TRUE;