feat(accounting): implement accountant's spec sheet — split fees, branch policy, government withholding

Sheraton's accountant handed over a 274-row spec for tomorrow's meeting.
Most of it was already correct (payroll, rentals, academies); this closes
the concrete gaps and builds the tools for the parts that are policy
decisions, not code.

ADDITION-FEE REVENUE SPLIT (spec rows 72-88)
The spec asks for the fee split "according to the ratio of the revenue"
without ever giving a ratio — but the ratio already existed:
ChildFeeCalculator/SpouseFeeCalculator compute a membership-value
component, a form-fee component and an annual-subscription component on
every addition. It just wasn't persisted past the display breakdown, so
by payment time nothing to split by. Now stored (fee_component_*
columns) and posted as three separate credits instead of one lump
"dependant addition" line, with a safety check that skips the split
(falls through unchanged) if the collected amount doesn't match the
stored components exactly.

MEMBERSHIP-FORM STAMP FEE (row 12)
BillingService's own price breakdown already reads "form fee: 500 —
stamp: 5" — the 505 EGP was never wrong, accounting just credited all of
it to form revenue. Now splits the 5 EGP to the government stamp
liability that already existed in the chart, unused
(23082103 طابع الشهداء). Only fires where a branch has it configured —
every other branch posts exactly as before.

BRANCH FEE SETTINGS — a real tool, not a guess
The spec argues with itself about several fees: "add this at Sheraton"
against "cancel it everywhere" in consecutive lines, "each branch has
its own card-commission rate" with a rate given for exactly one branch.
/accounting/branch-fees is where that gets decided per branch or once
for all of them, with a one-click "generalize to every branch" action —
covers the stamp fee, cheque clearing fee, bounced-cheque fee, and a
tiered card commission (threshold + rate + whole-vs-excess basis, with
a live preview). Seeded active for Sheraton with the exact figures the
spec gives; every other branch starts with nothing configured.

CARD COMMISSION — posted as an expense, not left in the bank figure
Implemented as a small adjusting entry after the main collection posts
(Dr commission expense / Cr the same card account, reclassifying part of
what was already debited) rather than rewritten into ~30 payment types'
posting logic. Verified: 50,000 EGP visa payment above a 10,000
threshold at 2% posts exactly 800.00, non-visa payments are untouched,
replay does not double-post.

GOVERNMENT WITHHOLDING ON EXPENSES (rows 223-264)
Ordinary stamp duty, additional stamp duty, commercial-profits
withholding — deducted at source from every vendor invoice, reusing
liability accounts the chart already had unused (23081202-23081204).
Rates are not guessed: Egyptian withholding schedules are progressive
law, not a percentage this migration could safely invent, so it ships
at 0% and inactive until finance sets real rates on the same settings
screen. Accounts payable now records the NET amount owed after
withholding, which is what the club actually pays.

CASH DISBURSEMENT BANNED FOR EXPENSES (rows 190-191)
"As a government institution, cash disbursement is forbidden — every
expense by cheque." Enforced once, at VendorPaymentService::createPayment,
with a system_config kill switch for the day this genuinely needs an
exception (logged as a deliberate override, not a silent bypass).

NOTES PAYABLE — cheques now a liability until the bank clears them
onVendorPaymentCompleted was crediting Bank directly the moment a
cheque was issued, before the bank had paid anything. Now credits
أوراق دفع (notes payable) instead, and /accounting/notes-payable is the
monthly reconciliation the spec asks for at rows 267-269: pick the
cheques the bank statement confirms cleared, post one closing entry.
Zero live vendor payments existed, so this changes no historical data.

Verified end-to-end against a scratch copy of production: every
scenario checked exactly against hand-computed expected values (not
just "it posted something") — split amounts, commission arithmetic,
withholding math, net payable — trial balance nets to 0.00, zero
unbalanced entries, zero postings to header accounts, every path
idempotent under replay.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>