Add store loan methods with public website calculate API.

Supports dashboard CRUD and tenant list/get/calculate so storefronts can offer installments, requiring a method pick when several exist.

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

database/migrations/098_store_loan_methods.sql

@@ -0,0 +1,37 @@
+-- Store loan / installment methods (اقساط و تسهیلات)
+
+CREATE TABLE IF NOT EXISTS store_loan_methods (
+  id BIGSERIAL PRIMARY KEY,
+  business_id BIGINT NOT NULL REFERENCES businesses (id) ON DELETE CASCADE ON UPDATE NO ACTION,
+  name VARCHAR(255) NOT NULL,
+  name_en VARCHAR(255) NOT NULL,
+  description TEXT NULL,
+  image_media_id BIGINT NULL REFERENCES media (id) ON UPDATE NO ACTION,
+  image_aspect_ratio VARCHAR(10) NOT NULL DEFAULT '1:1',
+  min_shopping_amount NUMERIC(12, 2) NOT NULL,
+  min_amount NUMERIC(12, 2) NOT NULL,
+  max_amount NUMERIC(12, 2) NOT NULL,
+  interest NUMERIC(8, 4) NOT NULL,
+  return_months_min INT NOT NULL,
+  return_months_max INT NOT NULL,
+  return_months_step INT NOT NULL DEFAULT 3,
+  sort_order INT NOT NULL DEFAULT 0,
+  is_active BOOLEAN NOT NULL DEFAULT TRUE,
+  created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+  updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+CREATE INDEX IF NOT EXISTS idx_store_loan_methods_business_id
+  ON store_loan_methods (business_id);
+
+CREATE INDEX IF NOT EXISTS idx_store_loan_methods_image_media_id
+  ON store_loan_methods (image_media_id);
+
+CREATE INDEX IF NOT EXISTS idx_store_loan_methods_business_sort_order
+  ON store_loan_methods (business_id, sort_order);
+
+DROP TRIGGER IF EXISTS store_loan_methods_set_updated_at ON store_loan_methods;
+CREATE TRIGGER store_loan_methods_set_updated_at
+  BEFORE UPDATE ON store_loan_methods
+  FOR EACH ROW
+  EXECUTE FUNCTION set_updated_at();