iter mq.1: class-ref canonical-form extension + workspace-internal class-name qualification

Three schema fields move bare → canonical (bare for same-module,
<module>.<Class> for cross-module): InstanceDef.class,
Constraint.class, SuperclassRef.class. Symmetric to ct.1's
Type::Con.name rule. ClassDef.name stays bare.

validate_canonical_type_names gains three field-walks via new
check_class_ref helper + two sibling diagnostics
BareCrossModuleClassRef / BadCrossModuleClassRef.
check_class_name_fields narrowed to ClassDef.name-only.

Workspace-internal class-name keys all qualified:
class_def_module, class_by_name, registry entries.0,
ClassMethodEntry.class_name, class_superclasses, mono's
class_index, Origin::Class.class_name. New qualify_class_ref
helper at workspace.rs scope plus sibling
qualify_class_ref_in_check in ailang-check.

Two new positive on-disk fixtures (mq1_xmod_constraint_class{,_dep})
exercise the qualified Constraint.class shape.

Recon claim that all existing fixtures' class-refs are intra-module
was empirically wrong — 10 fixtures required minimal canonical-form
migration. Duplicate-instance test architecturally restructured:
post-mq.1 orphan-freedom makes two-modules-on-same-(class,type)
structurally impossible; new test_22b1_dup_same_module fixture
lands both instances in the class's module.

Plan defects fixed inline: Origin::Class.class_name single
construction site (plan recon off-by-one); build_class_index in
mono.rs needed qualifying; build_module_globals needed Def::Instance
carve-out; check_fn declared-constraint matching needed inline
canonical-form lifting; NoInstance Float-aware message arm needed
prelude.Eq/prelude.Ord match; coherence type-leg needed qualified-
head split-and-lookup. Tasks 3-6 ran as one coherent fix.

7/7 tasks, 520 tests green. bench/compile_check.py + cross_lang.py
exit 0; bench/check.py exit 1 (4 improvements-beyond-tolerance,
audit-ratifiable, not a regression).

MethodNameCollision + dispatch path unchanged; iters mq.2 + mq.3
land them.

crates/ailang-core/src/ast.rs

@@ -258,7 +258,13 @@ pub struct Suppress {
 /// pre-22b hashes.
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct ClassDef {
-    /// Class name (capitalised by convention).
+    /// Class name (capitalised by convention). Bare — symmetric to
+    /// `TypeDef.name`, the field is the defining-site context, not
+    /// a reference. Cross-module class references live in
+    /// `InstanceDef.class`, `Constraint.class`, and
+    /// `SuperclassRef.class`; those fields carry the canonical form
+    /// (bare for same-module, `<module>.<Class>` for cross-module)
+    /// per mq.1.
     pub name: String,
     /// Single type-parameter name.
     pub param: String,
@@ -275,7 +281,9 @@ pub struct ClassDef {
 /// Iter 22b.1: reference to a superclass relation in [`ClassDef`].
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct SuperclassRef {
-    /// Superclass name.
+    /// Superclass name in canonical form (mq.1): bare for a
+    /// same-module class, `<module>.<Class>` for a cross-module
+    /// class. Symmetric to ct.1's `Type::Con.name` rule.
     pub class: String,
     /// Type the superclass is applied to. MUST equal the parent
     /// `ClassDef.param` (validated in 22b.2 — schema does not enforce).
@@ -310,7 +318,9 @@ pub struct ClassMethod {
 /// overrides of default-bearing methods.
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct InstanceDef {
-    /// Class being instantiated.
+    /// Class being instantiated, in canonical form (mq.1): bare for
+    /// a same-module class, `<module>.<Class>` for a cross-module
+    /// class. Symmetric to ct.1's `Type::Con.name` rule.
     pub class: String,
     /// Concrete type the class is applied to.
     #[serde(rename = "type")]
@@ -341,7 +351,9 @@ pub struct InstanceMethod {
 /// matching registry entry exists.
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct Constraint {
-    /// Class name.
+    /// Class name in canonical form (mq.1): bare for a same-module
+    /// class, `<module>.<Class>` for a cross-module class.
+    /// Symmetric to ct.1's `Type::Con.name` rule.
     pub class: String,
     /// Type the class is applied to.
     #[serde(rename = "type")]