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_llvm_codegen.py

@@ -25,7 +25,7 @@ def test_llvm_hello_world_structure():
     llvm_ir = generate_llvm_ir(ir_dict)
 
     # Check basic LLVM IR structure
-    assert "define void @render_HelloWorld()" in llvm_ir
+    assert "define i32 @render_HelloWorld()" in llvm_ir
     assert "ret void" in llvm_ir
 
     # Should have string constants
@@ -115,10 +115,12 @@ def test_llvm_ir_syntax_valid():
     llvm_ir = generate_llvm_ir(ir_dict)
 
     # Basic syntax checks
-    assert llvm_ir.count("define") == llvm_ir.count("ret void")  # All functions return
+    assert llvm_ir.count("define") == llvm_ir.count("ret")  # All functions have returns
     assert "%" in llvm_ir  # Has SSA variables
     assert "call" in llvm_ir  # Has function calls
     assert "@" in llvm_ir  # Has global symbols
+    assert "define void @main()" in llvm_ir  # Has main entry point
+    assert "define i32 @render_" in llvm_ir  # Component functions return i32
 
 
 def test_llvm_ir_compiles_with_llc():