Reusable account-P&L bounds for spot funds.

With a known effective account currency, an account-tier mismatch fails closed and blocks the account; account-group and global mismatches are skipped. A known-currency account with no account barrier and no matching fallback has no effective barrier, but its P&L keeps accumulating and publishing. Without an effective currency, the first in-scope barrier applies. Bounds are compared as stored and are never FX-converted. At least one bound must be present when the barrier is registered with a builder or configurator.