feat(market): FIFA 5% transfer fee policy, host settle_sale capability, isolated staging harness

Core gains the generic settlement (gitlink 31ab4a6); the FIFA-specific parts live
here.

FEE (openfut-adapter-fifa17/src/fut/economy_policy.rs), beside pack_price and
match_reward_total because 5% is a game policy constant and Core must stay
game-neutral — Core only validates 0 <= fee <= gross and never computes a rate:

  TRANSFER_MARKET_FEE_PERCENT = 5
  transfer_market_fee(gross)  = floor(gross * 5 / 100), i128 intermediate
  seller_proceeds(gross)      = gross - fee

Integer only. Floating point is never used for coin settlement: 0.05 is not
representable in binary and a f64 round trip can create or destroy a coin at large
prices. Widening to i128 makes overflow unreachable for any i64 price, so no price
ceiling has to be assumed.

ROUNDING IS A CHOICE AND IT IS NOT CONFIRMED. The fee is floored, so the seller
keeps the fractional coin, chosen because it makes fee + proceeds == gross hold
exactly at every input — the property the accounting invariant rests on. The
discriminating case against flooring the seller's 95% instead is a gross of 150:
this rule pays 143, the alternative 142. Nothing in the corpus or the client binary
settles which the real server did (the client is only ever told the gross; no
tax/netPrice/sellerProceeds wire field exists). Pinned at 0/1/19/20/21/39/40/100/
150/200/1_000/15_000/15_000_000/i64::MAX plus a fee+proceeds==gross sweep.

HOST: CoreEconomy gains settle_sale + EconomySale/EconomySaleReceipt, implemented on
HttpCoreClient as POST /economy/settle-sale. Request field names were checked
against Core's actual SettleSaleRequest/SaleReceipt rather than assumed. Absent club
ids are OMITTED from the body (not null), which is what Core's Outside/active-club
defaults depend on, so a unit test pins that body shape. handle_market_buy is
deliberately untouched: the synthetic buy path has no counterparty, so minting there
is correct.

HARNESS: scripts/settlement-staging.py, stdlib only, drives a REAL Core over real
HTTP on an ephemeral port against a throwaway DB (production 8099/8199/18080 in a
hard deny-list checked in three places), seeds the canonical two-party fixture,
prints BEFORE/PURCHASE/AFTER with PASS-FAIL lines, cleans up in a finally. 31/31
pass. It found the rejection-precedence bug fixed in Core, and that Core's content
preflight aborts startup on an owned card whose CardDefinitionId no pack defines.

Gates: Core 194, adapter 217, host 127, harness 31/31, clippy clean, new code
fmt-clean. Nothing deployed; no production process, port or database was touched.

openfut-utas-host/src/economy_store.rs

@@ -457,7 +457,7 @@ mod tests {
     use std::collections::HashMap;
     use std::sync::atomic::{AtomicI64, AtomicU32, Ordering};
 
-    use crate::{EconomyEntitlement, EconomyPurchase};
+    use crate::{EconomyEntitlement, EconomyPurchase, EconomySale, EconomySaleReceipt};
 
     // ── Recording economy double ────────────────────────────────────────────
 
@@ -588,6 +588,10 @@ mod tests {
             self.purchased.lock().push((cost, items.to_vec()));
             Ok(self.balance.fetch_sub(cost, Ordering::SeqCst) - cost)
         }
+        fn settle_sale(&self, _sale: &EconomySale<'_>) -> Result<EconomySaleReceipt, CoreError> {
+            // Sale settlement is not exercised by the Store/quick-sell paths.
+            Err(CoreError::Status(501))
+        }
     }
 
     // ── Identity / entity / lookup doubles ──────────────────────────────────