Fix nested components - render functions now return i32

Changes:
- Component render functions return i32 (root element) instead of void
- Nested components (yield SomeComponent()) now work correctly
- Added main() entry point that calls top-level component and sets root
- Updated runtime to call main() instead of render_ComponentName()

Note: Active state in ternary expressions still needs reactive updates
This commit fixes the nested component rendering issue

All tests passing (51 passed, 2 skipped)

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

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

tests/test_wrapper_components.py

@@ -76,7 +76,7 @@ def SimpleTabs():
     llvm_ir = generate_llvm_ir(ir)
 
     # Should generate render function for TabButton with parameters
-    assert "define void @render_TabButton(" in llvm_ir
+    assert "define i32 @render_TabButton(" in llvm_ir
 
     # Should call TabButton from SimpleTabs with arguments
-    assert "call void @render_TabButton(" in llvm_ir
+    assert "call i32 @render_TabButton(" in llvm_ir