feat: Implement Phase 9.78e instance_v2 migration with unified registry

Major achievements:
- ✅ UserDefinedBoxFactory implementation with unified registry integration
- ✅ Constructor execution for user-defined boxes (Person init working)
- ✅ Import path fixes across interpreter modules
- ✅ unwrap_instance helper function for InstanceBox operator support

Technical details:
- Modified UnifiedBoxRegistry to handle empty box_types() factories
- Implemented constructor execution in execute_new for InstanceBox
- Added unwrap_instance helper to handle InstanceBox wrapping in operators
- Updated CURRENT_TASK.md with detailed progress tracking

Next: Fix 4 operator functions to complete InstanceBox operator support

🤖 Generated with [Claude Code](https://claude.ai/code)

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

src/box_factory/mod.rs

@@ -90,10 +90,22 @@ impl UnifiedBoxRegistry {
         }
         drop(cache);
         
-        // Fallback: linear search through all factories
+        // Linear search through all factories
         for factory in &self.factories {
-            if factory.box_types().contains(&name) && factory.is_available() {
-                return factory.create_box(name, args);
+            if !factory.is_available() {
+                continue;
+            }
+            
+            // For factories that advertise types, check if they support this type
+            let box_types = factory.box_types();
+            if !box_types.is_empty() && !box_types.contains(&name) {
+                continue;
+            }
+            
+            // Try to create the box (factories with empty box_types() will always be tried)
+            match factory.create_box(name, args) {
+                Ok(boxed) => return Ok(boxed),
+                Err(_) => continue, // Try next factory
             }
         }