Phase 1 of the accounts/controller refactor. Moves the six pure
list-level validators (validate_disabled_accounts, validate_accounting_period,
validate_cwip_accounts, check_freezing_date, validate_against_pcv,
validate_allowed_dimensions) out of general_ledger.py into the new
erpnext/accounts/services/gl_validator.py. general_ledger.py imports and
calls them at the existing sites; no behavior change (Phase 0 GL snapshots
remain byte-identical).
The debit/credit balance trio stays in general_ledger.py for now since
get_debit_credit_difference mutates entries and is interleaved with the
round-off repair.
Phased plan to decompose accounts_controller.py and the sales_invoice.py
monolith into composed services. Documents the frozen GL-layer design
(GLComposer / gl_validator / general_ledger sink), method bucketing, and
the 8-phase rollout.
