WIP: Phase 9.78b - Unified registry integration (import issues pending)

Progress made:
- Add unified registry call to objects.rs execute_new() method
- Initialize unified registry in runner.rs on startup
- Create global registry management in runtime/unified_registry.rs
- Add test case for unified registry validation
- Implement fallback to legacy match statement for compatibility

Current issue:
- Module import errors in runtime/unified_registry.rs preventing build
- Need to resolve box_factory module path visibility from runtime context

Next steps:
- Fix import paths for box_factory modules
- Test unified registry functionality
- Remove legacy match statement after validation

Technical details:
- execute_new() now tries unified registry first, falls back to legacy
- Registry initialized with BuiltinBoxFactory and PluginBoxFactory
- Maintains backward compatibility during transition

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

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

local_tests/test_unified_registry.nyash

@@ -0,0 +1,16 @@
+# Phase 9.78b: Unified BoxFactory Registry test
+
+# Test basic Box creation through unified registry
+local str = new StringBox("Hello UnifiedBox!")
+print(str.to_string_box().value)
+
+local num = new IntegerBox(42)
+print(num.to_string_box().value)
+
+local flag = new BoolBox(true)
+print(flag.to_string_box().value)
+
+local arr = new ArrayBox()
+print("ArrayBox created: " + arr.type_name())
+
+print("🎉 All unified registry tests passed!")