feat(scout_access): optional cross-contract player validation on pay_to_contact

[gracious01-tech]

Summary

Adds an optional cross-contract player existence check to pay_to_contact. When the registration contract address is configured via the new set_registration_contract admin function, the scout access contract validates that the target player_id exists before collecting any fee or creating a contact record. When the address is not set the existing behaviour is fully preserved.

Changes

contracts/scout_access/src/errors.rs

• Added PlayerNotFound = 13 to ScoutAccessError

contracts/scout_access/src/types.rs

• Added DataKey::RegistrationContract variant

contracts/scout_access/src/lib.rs

• Added PERSISTENT_TTL_MIN / PERSISTENT_TTL_MAX constants (were referenced but never declared — pre-existing bug fixed)
• Added mod progress_contract { contractimport!(...) } (same pre-existing missing declaration fixed)
• Added mod registration_contract { contractimport!(...) } for the new cross-contract client
• Added set_registration_contract(env, addr) admin function — stores the registration contract address in DataKey::RegistrationContract (admin auth required)
• In pay_to_contact: after the duplicate-contact guard, optionally calls registration_contract::Client::try_get_player(&player_id); returns PlayerNotFound and aborts before any XLM transfer if the lookup fails; skips the check entirely when no address is stored
• Added two unit tests:
  • test_pay_to_contact_without_registration_contract_skips_validation — no registration contract set; contact with a non-existent player_id succeeds
  • test_pay_to_contact_with_registration_contract_rejects_unknown_player — registration contract wired; contact with a non-existent player_id panics with PlayerNotFound

contracts/scout_access/Cargo.toml

• Added scoutchain-registration = { path = "../registration" } as a dev-dependency so tests can register the contract directly via env.register_contract

.github/workflows/contract-ci.yml

• Moved the WASM build step before cargo test — contractimport! reads the WASM at compile time so tests cannot compile without the artefacts present

Validation logic

pay_to_contact(scout, player_id)
  ├── require_not_paused
  ├── scout.require_auth
  ├── require_active_subscription
  ├── guard: AlreadyContacted
  ├── [if RegistrationContract set]
  │     └── try_get_player(player_id) → Err → return PlayerNotFound (no fee collected)
  ├── transfer contact_fee_stroops XLM
  ├── accumulate_fee
  ├── write ContactRecord
  └── emit player_contacted event

Testing

Test	Registration contract set	Expected result
test_pay_to_contact_without_registration_contract_skips_validation	No	Contact succeeds for any player_id
test_pay_to_contact_with_registration_contract_rejects_unknown_player	Yes (empty registry)	Panics with PlayerNotFound

All existing tests are unaffected — no production logic outside pay_to_contact was changed.