## Why

Account statistics are fixed mall fixtures, and points redemption needs an auditable balance rather than mutable user fields. A customer account boundary establishes safe balances and append-only history before any points-spend flow is introduced.

## What Changes

- Add one customer account per supported balance: cash balance, frozen cash, and integer loyalty points.
- Add append-only account entries that record the resulting balance, signed delta, reason, reference type, and reference ID.
- Add an authenticated customer account summary endpoint and replace the account-stat fixture on the mall user center.
- Provide transactional service operations for later flows to credit, debit, freeze, and release funds or points with non-negative-balance checks.

## Capabilities

### New Capabilities
- `customer-accounts`: Customer balance and points accounts, immutable entries, account summary, and guarded balance mutations.

### Modified Capabilities
- `frontend-mall`: User-center account statistics load through the shared API client.

## Non-goals

No top-up, payment-from-balance, withdrawal, refund-to-balance, points earning campaign, merchant settlement, or public account-entry listing is included. The frozen monetary kind is reserved for later freeze/release flows.

## Impact

Adds Rust account module and migrations, shared account types/API/locales, a mall live-data migration, and a reusable transactional dependency for the points mall.