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>

Cargo.lock

@@ -306,6 +306,7 @@ dependencies = [
  "arje-cas",
  "base64 0.22.1",
  "bincode",
+ "brahman-cards",
  "postcard",
  "serde",
  "serde_json",
@@ -1720,6 +1721,7 @@ dependencies = [
 name = "brahman-cards"
 version = "0.1.0"
 dependencies = [
+ "anyhow",
  "brahman-card",
  "chasqui-card",
  "nahual-meta-schema",