feat(nakui-ui): migrar consumer al brazo brahman_cards::load_cards_from_dir

Primera consumer migration del brazo. nakui-ui ya no llama a
nakui_ui_schema::load_modules_from_dir directamente; pasa por
brahman_cards::load_cards_from_dir y extrae UiModule del CardBody.

Beneficios concretos:
- Soporta .ncl además de .json (templates Nickel + merge funcionan
  en cualquier subdir de modules).
- Cards de otros body kinds (Ente/Monad) se skipean limpio con
  toast informativo, no rompen la carga.

Cambios en brahman-cards:
- Nuevo load_cards_from_dir(dir) + variante con readers/filenames
  custom. DEFAULT_CARD_FILENAMES = [card.ncl, card.json, module.ncl,
  module.json] (orden de prioridad).
- 4 tests nuevos del helper.

Cambios en nakui-ui:
- Nueva dep brahman-cards.
- Helper load_ui_modules(dir) -> (Vec<Module>, Vec<String>) envuelve
  el brazo, filtra a UiModule, aplica Module::validate(), detecta
  duplicate ids.
- MetaUi::new usa el helper, emite toast con cards skipped si las hay.
- 3 tests e2e nuevos.

26/26 brahman-cards verdes (+4). 48/48 nakui-ui verdes (+3).
Workspace build verde.

nakui_ui_schema::load_modules_from_dir queda intacto (sus tests lo
usan + otros consumers futuros pueden preferirlo). Migración opt-in.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/core/brahman-cards/tests/integration.rs

@@ -268,6 +268,142 @@ fn extensions_field_starts_empty_in_v1() {
     assert_eq!(card.extensions, BTreeMap::new());
 }
 
+// ===========================================================================
+// load_cards_from_dir (subdir walking)
+// ===========================================================================
+
+#[test]
+fn load_cards_from_dir_walks_subdirs_and_finds_module_json() {
+    let root = unique_dir("dir-walk");
+    // Subdir A: tiene module.json (UiModule).
+    let a = root.join("alpha");
+    std::fs::create_dir(&a).unwrap();
+    std::fs::write(
+        a.join("module.json"),
+        serde_json::to_vec_pretty(&json!({
+            "id": "alpha",
+            "label": "Alpha",
+            "entities": [],
+            "menu": [],
+            "views": {}
+        }))
+        .unwrap(),
+    )
+    .unwrap();
+    // Subdir B: tiene module.json (UiModule).
+    let b = root.join("bravo");
+    std::fs::create_dir(&b).unwrap();
+    std::fs::write(
+        b.join("module.json"),
+        serde_json::to_vec_pretty(&json!({
+            "id": "bravo",
+            "label": "Bravo",
+            "entities": [],
+            "menu": [],
+            "views": {}
+        }))
+        .unwrap(),
+    )
+    .unwrap();
+    // Subdir C: NO tiene ninguno de los filenames convencionales —
+    // se debe skipear sin error.
+    let c = root.join("charlie");
+    std::fs::create_dir(&c).unwrap();
+    std::fs::write(c.join("readme.txt"), b"sin card aca").unwrap();
+
+    let cards = brahman_cards::load_cards_from_dir(&root).expect("ok");
+    let ids: Vec<&str> = cards.iter().map(|c| c.id.as_str()).collect();
+    assert_eq!(
+        ids,
+        vec!["alpha", "bravo"],
+        "orden lexicográfico por subdir name"
+    );
+    for c in &cards {
+        assert_eq!(c.body.kind_name(), "ui_module");
+    }
+
+    std::fs::remove_dir_all(&root).ok();
+}
+
+#[test]
+fn load_cards_from_dir_prefers_ncl_over_json_when_both_present() {
+    let root = unique_dir("dir-prefer");
+    let sub = root.join("only");
+    std::fs::create_dir(&sub).unwrap();
+    // Ambos archivos existen; el .ncl debería ganar.
+    std::fs::write(
+        sub.join("card.ncl"),
+        r#"{ id = "from_ncl", label = "Ncl", entities = [], menu = [], views = {} }"#,
+    )
+    .unwrap();
+    std::fs::write(
+        sub.join("card.json"),
+        serde_json::to_vec(&json!({
+            "id": "from_json",
+            "label": "Json",
+            "entities": [], "menu": [], "views": {}
+        }))
+        .unwrap(),
+    )
+    .unwrap();
+
+    let cards = brahman_cards::load_cards_from_dir(&root).expect("ok");
+    assert_eq!(cards.len(), 1);
+    assert_eq!(cards[0].id, "from_ncl", "card.ncl tiene prioridad");
+
+    std::fs::remove_dir_all(&root).ok();
+}
+
+#[test]
+fn load_cards_from_dir_propagates_per_file_errors_loud() {
+    let root = unique_dir("dir-error-loud");
+    let sub = root.join("broken");
+    std::fs::create_dir(&sub).unwrap();
+    std::fs::write(sub.join("card.json"), b"{ this is not valid json").unwrap();
+
+    let err = brahman_cards::load_cards_from_dir(&root).unwrap_err();
+    assert!(
+        matches!(err, CardLoadError::JsonParse(_)),
+        "el error de un file roto debe propagar fail-loud, got {err:?}"
+    );
+
+    std::fs::remove_dir_all(&root).ok();
+}
+
+#[test]
+fn load_cards_from_dir_with_custom_filenames() {
+    let root = unique_dir("dir-custom-fname");
+    let sub = root.join("only");
+    std::fs::create_dir(&sub).unwrap();
+    // Filename custom que NO está en el default.
+    std::fs::write(
+        sub.join("manifest.json"),
+        serde_json::to_vec(&json!({
+            "id": "x",
+            "label": "X",
+            "entities": [], "menu": [], "views": {}
+        }))
+        .unwrap(),
+    )
+    .unwrap();
+
+    // Default no encuentra nada (skipea):
+    let with_default = brahman_cards::load_cards_from_dir(&root).unwrap();
+    assert_eq!(with_default.len(), 0, "default filenames no incluye manifest.json");
+
+    // Custom filename encuentra:
+    let with_custom = brahman_cards::load_cards_from_dir_with(
+        &root,
+        &["manifest.json"],
+        &brahman_cards::default_readers(),
+    )
+    .unwrap();
+    assert_eq!(with_custom.len(), 1);
+    assert_eq!(with_custom[0].id, "x");
+
+    std::fs::remove_dir_all(&root).ok();
+}
+
 // ===========================================================================
 // Helpers de tests
 // ===========================================================================
@@ -281,3 +417,18 @@ fn tempfile_path(name: &str) -> std::path::PathBuf {
     ));
     p
 }
+
+fn unique_dir(name: &str) -> std::path::PathBuf {
+    let mut p = std::env::temp_dir();
+    p.push(format!(
+        "brahman-cards-test-{}-{}-{}",
+        std::process::id(),
+        std::time::SystemTime::now()
+            .duration_since(std::time::UNIX_EPOCH)
+            .map(|d| d.as_nanos())
+            .unwrap_or(0),
+        name
+    ));
+    std::fs::create_dir_all(&p).unwrap();
+    p
+}