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_component_props.py

@@ -57,7 +57,7 @@ def Button(label):
     llvm_ir = generate_llvm_ir(ir)
 
     # Should generate render function with parameter
-    assert "define void @render_Button(i32 %label)" in llvm_ir
+    assert "define i32 @render_Button(i32 %label)" in llvm_ir
 
 
 def test_parse_yield_component_with_args():
@@ -111,8 +111,8 @@ def Parent():
     components = parse_component(source)
     llvm_ir = generate_llvm_ir(components)
 
-    # Should call render_Child with argument
-    assert "call void @render_Child(i32 42)" in llvm_ir
+    # Should call render_Child with argument and capture return value
+    assert "call i32 @render_Child(i32 42)" in llvm_ir
 
 
 def test_component_with_default_param():
@@ -180,7 +180,7 @@ def Counter(initial_count):
     llvm_ir = generate_llvm_ir(ir)
 
     # Should accept parameter
-    assert "define void @render_Counter(i32 %initial_count)" in llvm_ir
+    assert "define i32 @render_Counter(i32 %initial_count)" in llvm_ir
 
     # Signal should be initialized with parameter value
     # This will require storing the param value to the signal global