feat(payments): add the payments schema, currency domain and money type

Stand up the payments data foundation: a self-contained `payments` Postgres
schema for the in-game currency, wallets, benefits, catalog, orders and the
append-only operations ledger, behind a domain package — nothing wired to real
money yet.

- Migration 00010: the `payments` schema and a NOLOGIN confinement role (ALL on
  payments.*, nothing on backend); the ledger with a BEFORE UPDATE/DELETE
  append-only trigger and a partial idempotency index; the materialised
  balances/benefits; the catalog (atoms seeded) + products + per-method prices;
  the typed single-row config; orders and payment_events. There is no
  cross-schema foreign key — account_id is a plain uuid kept consistent in code,
  which keeps the domain extractable. Expand-contract and reversible.
- Money is a bigint in the currency's minor units carried by a `Money` value
  type (exact, math/big): no float ever touches an amount, and a whole-unit
  currency cannot hold a fraction.
- Extend jetgen to generate the payments schema; construct the service in the
  composition root behind a narrow interface with a boot reachability check.
- Tests: integration (role confinement via SET ROLE, the append-only trigger,
  CHECK constraints, the idempotency index, and a forward+backward migration),
  Money unit tests, and an import-boundary test keeping the payments jet code
  private to the domain.
- Docs: PLAN.md, docs/PAYMENTS.md (+ _ru mirror) updated to the built model.

backend/internal/postgres/jet/payments/table/product.go

@@ -0,0 +1,90 @@
+//
+// Code generated by go-jet DO NOT EDIT.
+//
+// WARNING: Changes to this file may cause incorrect behavior
+// and will be lost if the code is regenerated
+//
+
+package table
+
+import (
+	"github.com/go-jet/jet/v2/postgres"
+)
+
+var Product = newProductTable("payments", "product", "")
+
+type productTable struct {
+	postgres.Table
+
+	// Columns
+	ProductID postgres.ColumnString
+	Title     postgres.ColumnString
+	Active    postgres.ColumnBool
+	CreatedAt postgres.ColumnTimestampz
+	UpdatedAt postgres.ColumnTimestampz
+
+	AllColumns     postgres.ColumnList
+	MutableColumns postgres.ColumnList
+	DefaultColumns postgres.ColumnList
+}
+
+type ProductTable struct {
+	productTable
+
+	EXCLUDED productTable
+}
+
+// AS creates new ProductTable with assigned alias
+func (a ProductTable) AS(alias string) *ProductTable {
+	return newProductTable(a.SchemaName(), a.TableName(), alias)
+}
+
+// Schema creates new ProductTable with assigned schema name
+func (a ProductTable) FromSchema(schemaName string) *ProductTable {
+	return newProductTable(schemaName, a.TableName(), a.Alias())
+}
+
+// WithPrefix creates new ProductTable with assigned table prefix
+func (a ProductTable) WithPrefix(prefix string) *ProductTable {
+	return newProductTable(a.SchemaName(), prefix+a.TableName(), a.TableName())
+}
+
+// WithSuffix creates new ProductTable with assigned table suffix
+func (a ProductTable) WithSuffix(suffix string) *ProductTable {
+	return newProductTable(a.SchemaName(), a.TableName()+suffix, a.TableName())
+}
+
+func newProductTable(schemaName, tableName, alias string) *ProductTable {
+	return &ProductTable{
+		productTable: newProductTableImpl(schemaName, tableName, alias),
+		EXCLUDED:     newProductTableImpl("", "excluded", ""),
+	}
+}
+
+func newProductTableImpl(schemaName, tableName, alias string) productTable {
+	var (
+		ProductIDColumn = postgres.StringColumn("product_id")
+		TitleColumn     = postgres.StringColumn("title")
+		ActiveColumn    = postgres.BoolColumn("active")
+		CreatedAtColumn = postgres.TimestampzColumn("created_at")
+		UpdatedAtColumn = postgres.TimestampzColumn("updated_at")
+		allColumns      = postgres.ColumnList{ProductIDColumn, TitleColumn, ActiveColumn, CreatedAtColumn, UpdatedAtColumn}
+		mutableColumns  = postgres.ColumnList{TitleColumn, ActiveColumn, CreatedAtColumn, UpdatedAtColumn}
+		defaultColumns  = postgres.ColumnList{TitleColumn, ActiveColumn, CreatedAtColumn, UpdatedAtColumn}
+	)
+
+	return productTable{
+		Table: postgres.NewTable(schemaName, tableName, alias, allColumns...),
+
+		//Columns
+		ProductID: ProductIDColumn,
+		Title:     TitleColumn,
+		Active:    ActiveColumn,
+		CreatedAt: CreatedAtColumn,
+		UpdatedAt: UpdatedAtColumn,
+
+		AllColumns:     allColumns,
+		MutableColumns: mutableColumns,
+		DefaultColumns: defaultColumns,
+	}
+}