feat: support module-qualified constructor patterns in match expressions (issue 3)

Added module: Option<Ident> to Pattern::Constructor, updated parser to
handle module.Constructor(args) syntax in patterns, exported ADT
constructors from modules, and copied type definitions during module
import so types like Shape are usable in importing files.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/typechecker.rs

@@ -981,6 +981,13 @@ impl TypeChecker {
                     if !fields.is_empty() {
                         self.env.bind(&name, TypeScheme::mono(Type::Record(fields)));
                     }
+
+                    // Also copy type definitions so imported types are usable
+                    for (type_name, type_def) in &module_checker.env.types {
+                        if !self.env.types.contains_key(type_name) {
+                            self.env.types.insert(type_name.clone(), type_def.clone());
+                        }
+                    }
                 }
                 ImportKind::Direct => {
                     // Import a specific name directly
@@ -2476,7 +2483,7 @@ impl TypeChecker {
                 Vec::new()
             }
 
-            Pattern::Constructor { name, fields, span } => {
+            Pattern::Constructor { name, fields, span, .. } => {
                 // Look up constructor
                 // For now, handle Option specially
                 match name.name.as_str() {