iter ct.1.1: validator scaffolding + Type::Con canonical-form rules

Adds BareCrossModuleTypeRef / BadCrossModuleTypeRef / QualifiedClassName
to WorkspaceLoadError plus the validate_canonical_type_names function
that enforces the canonical-form rule on every Type::Con name reachable
from any def (including Term::Lam.param_tys / .ret_ty and Term::LetRec.ty).
Term::Ctor.type_name and class-name fields land in Tasks 2 + 3; the
validator is not yet wired into load_workspace (Task 6). Seven RED-first
unit tests cover the cases enumerated in spec section Testing strategy
plus a Lam-embedded-type smuggle-prevention test.

main.rs gains diagnostic arms for the three new variants to keep the
exhaustive match compiling.

crates/ail/src/main.rs

@@ -1153,6 +1153,55 @@ fn workspace_error_to_diagnostic(
                 "module": name,
             })),
         ),
+        // ct.1 (canonical-type-names): bare `Type::Con` that does not
+        // resolve to a primitive or a local TypeDef of the owning
+        // module. `candidates` lists qualified suggestions scanned
+        // from imports.
+        W::BareCrossModuleTypeRef { module, name, candidates } => Some(
+            ailang_check::Diagnostic::error(
+                "bare-cross-module-type-ref",
+                format!(
+                    "module `{module}` contains bare type name `{name}` that does not resolve to a local type; \
+                    candidates from imports: {candidates:?}"
+                ),
+            )
+            .with_ctx(serde_json::json!({
+                "module": module,
+                "name": name,
+                "candidates": candidates,
+            })),
+        ),
+        // ct.1: qualified `<owner>.<type>` where `<owner>` is not a
+        // known module or `<owner>` has no `TypeDef <type>`.
+        W::BadCrossModuleTypeRef { module, name } => Some(
+            ailang_check::Diagnostic::error(
+                "bad-cross-module-type-ref",
+                format!(
+                    "module `{module}` references qualified type `{name}` but the owner module is not known \
+                    or does not declare a type by that name"
+                ),
+            )
+            .with_ctx(serde_json::json!({
+                "module": module,
+                "name": name,
+            })),
+        ),
+        // ct.1: a class-reference field contains a `.` — class names
+        // are not module-qualified in this milestone.
+        W::QualifiedClassName { module, name, field } => Some(
+            ailang_check::Diagnostic::error(
+                "qualified-class-name",
+                format!(
+                    "module `{module}` contains qualified class name `{name}` in field `{field}`; \
+                    class names are not module-qualified in this milestone"
+                ),
+            )
+            .with_ctx(serde_json::json!({
+                "module": module,
+                "name": name,
+                "field": field,
+            })),
+        ),
     }
 }