refactor(loader): A3 — unificar loader, eliminar duplicación

El loader vivía partido: arje-brain/loader.rs cargaba EntityCards Y
Rules, mientras brahman-cards tenía su propia infra de card-loading.

Resolución por linaje:
- Card-loading (load_card_file, extract_card_from_json) → brahman-cards
  (entity_loader.rs). Toda card-loading del ecosistema vive ahí.
- Rule-loading (load_rules_file, extract_rules_from_json) → arje-brain-rules
  (loader.rs), junto a la definición de Rule.
- arje-brain/loader.rs eliminado.

arje-brain re-exporta ambos para compat de consumidores (arje-zero).
cargo check --workspace verde. Tests: 13 arje-brain-rules + 31 brahman-cards.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

crates/runtime/arje-brain/src/lib.rs

@@ -13,7 +13,6 @@
 pub mod introspect;
 pub mod autopromote;
 pub mod metrics;
-pub mod loader;
 
 // --- Re-export de los módulos de las 3 sub-crates ---
 pub use arje_brain_rules::{dispatch, engine, rules};
@@ -30,5 +29,9 @@ pub use audit::AuditLog;
 
 pub use autopromote::{spawn_autopromote_loop, AutopromoteParams};
 pub use introspect::{BrainState, IntrospectRequest, IntrospectResponse, IntrospectServer};
-pub use loader::{load_card_file, load_rules_file};
 pub use metrics::serve_metrics;
+
+// --- Loader: card-loading vive en brahman-cards, rule-loading en
+//     arje-brain-rules. Re-exportados aquí por compat de consumidores. ---
+pub use arje_brain_rules::{extract_rules_from_json, load_rules_file};
+pub use brahman_cards::{extract_card_from_json, load_card_file};