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/ast.rs

@@ -697,8 +697,9 @@ pub enum Pattern {
     Var(Ident),
     /// Literal: 42, "hello", true
     Literal(Literal),
-    /// Constructor: Some(x), None, Ok(v)
+    /// Constructor: Some(x), None, Ok(v), module.Constructor(x)
     Constructor {
+        module: Option<Ident>,
         name: Ident,
         fields: Vec<Pattern>,
         span: Span,