fifa17: price quick-sell from the client's own discard table

Quick-sell paid an invented five-tier rating ladder (its own comment said
"PLACEHOLDER, not EA-authentic"). It was blind to card type and rareflag, so a
94-rated TOTW special and a 94-rated gold common both sold for 1500, and every
non-player -- whose Core overall is 0 -- sold for the flat 150 floor. The ladder
existed in three places (adapter wire, host payout, an integration test's private
copy), which is a drift waiting to happen.

Add openfut-adapter-fifa17::fut::discard: the client's own fcc_discardcoins
table and its formula, round_half_up(rating * price / 100), keyed
(cardtype, level, rare). All of it is already reversed in
plan-2026-08-05-store-subsystem.md 3.6 and was verified there against 22 live
club items, 22 of 22 exact. DISCARD_COINS is generated from
fifa17-recon/data/tables/fcc_discardcoins.json and a test re-reads that file and
asserts row-for-row agreement, so the transcription cannot drift.

Collapse the three ladders into one method. ItemIdentityResolver::discard_value
both stamps the wire discardValue and prices the sale, because a non-zero
discardValue suppresses the client's local computation -- whatever is sent is
what the player is promised. The host's quick_sell_value is deleted and the
integration test's copy now calls the single implementation. A test with a
resolver double returning an impossible price proves the credit follows the wire;
reverting the payout to a ladder fails it.

Gated on OPENFUT_FIFA17_DISCARD_TABLE=1, default off: switching revalues the real
1991-item club 10.5x (1,820,400 -> 19,128,955 coins if wholly liquidated), up for
specials and DOWN for consumables, which the ladder overpaid 5.5x. That is an
operator's decision.

Staff decline to the ladder rather than pay 0: the client re-rates cardtypes
2/3/4/5/10 from its own DB and their rating is not imported. Deliberately not
guessed -- see the falsifier in the doc.

Verified on staging with the real club, both modes: flag off 1500 wire / 1500
paid; flag on 23760 wire / 23760 paid on an r99 rareflag-11 card (99*24000/100).
Consumables price from their catalog rating and agree with the client's own
computation. Adapter 244 lib tests, host 121 lib + 45 host_test, fmt and clippy
clean.

openfut-utas-host/tests/economy_concurrency.rs

@@ -226,16 +226,11 @@ fn set_balance(client: &HttpCoreClient, target: i64) {
     assert_eq!(client.balance().unwrap(), target, "balance set");
 }
 
-/// The on-wire quick-sell `discardValue` tiers (host `economy_store::quick_sell_value`),
-/// replicated to assert the EXACT credit — the client-visible contract.
+/// The on-wire quick-sell `discardValue`, taken from the ONE implementation the
+/// server uses rather than replicated here: a local copy silently passes while
+/// the real price changes underneath it.
 fn qs_value(rating: u8) -> i64 {
-    match rating {
-        r if r >= 85 => 1500,
-        r if r >= 80 => 900,
-        r if r >= 75 => 600,
-        r if r >= 65 => 300,
-        _ => 150,
-    }
+    openfut_adapter_fifa17::fut::item::legacy_discard_value(rating)
 }
 
 fn owns(client: &HttpCoreClient, core_id: &str) -> bool {