feat(adapter): FIFA17 squad extension v1 + full-replacement PUT builder

Add fut::squad_ext::Fifa17SquadExtensionV1 — the versioned, adapter-owned
payload Core stores opaquely alongside the canonical squad. Carries the
FIFA-only wire state that is not Core-canonical:
  - custom[]        opaque 33-int string, round-tripped verbatim
  - squad_type      observed FIFA token
  - kit_numbers     keyed by owned_card_id (kit follows the PLAYER, proven
                    by the swap/formation captures), never by slot/definition
  - manager         opaque item ref (not a squad player; not shaped)
  - kicktakers      opaque role refs; relationship to captain UNKNOWN, so
                    preserved verbatim and never normalized to the captain
  - client_reported chemistry/rating/starRating shadow, never authoritative
from_payload enforces the payload schema version first (distinct from Core's
DB schema); an unknown version is rejected, never coerced.

build_squad_write turns a parsed PUT + host wire->owned resolver into a
canonical ProposedSquad + extension, refusing on unresolved ids or a
duplicate owned item. Identity resolution is explicitly NOT authorization.

Refactor the 550a59d parser scaffold: ProposedSquad is now pure canonical
(FIFA-only + shadow fields moved to the extension); the canonical formation
is the FIFA wire token verbatim (drop the lossy f442->"4-4-2" map that
could not even represent f433) so formation and index round-trip exactly
with no derivation. Bench split is the fixed 23-slot array convention.

openfut-adapter-fifa17/src/fut/mod.rs

@@ -10,3 +10,4 @@ pub mod item;
 pub mod entities;
 pub mod owned_query;
 pub mod squad;
+pub mod squad_ext;