Integrate reactive rendering into _emit_if()

Modified _emit_if() to:
- Create marker node via js_create_marker()
- Append marker to parent element
- Store marker ID in global
- Call _init_conditional_X() to render and insert active branch

Branch render functions work correctly:
- Build element tree locally
- Return root element ID
- Called by init function to pre-render all branches

Fallback to _emit_if_static() if conditional not collected.

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

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

ritz/llvm_codegen_signals.py

@@ -461,7 +461,33 @@ class SignalLLVMIRGenerator:
         return None
 
     def _emit_if(self, stmt: dict[str, Any]) -> str | None:
-        """Emit an if statement."""
+        """Emit an if statement with reactive rendering."""
+        # Get conditional ID from our collected conditionals
+        cond_id = self.conditional_map.get(id(stmt))
+
+        if cond_id is None:
+            # Fallback to static rendering if not collected (shouldn't happen)
+            return self._emit_if_static(stmt)
+
+        # Create marker node
+        marker_var = self._new_var()
+        self.lines.append(f"  %{marker_var} = call i32 @js_create_marker()")
+
+        # Append marker to parent if we have one
+        if self.parent_element_stack:
+            parent_var = self.parent_element_stack[-1]
+            self.lines.append(f"  call void @js_append_child(i32 %{parent_var}, i32 %{marker_var})")
+
+        # Store marker ID in global
+        self.lines.append(f"  store i32 %{marker_var}, i32* @cond_{cond_id}_marker")
+
+        # Call init function to render and insert active branch
+        self.lines.append(f"  call void @_init_conditional_{cond_id}()")
+
+        return None
+
+    def _emit_if_static(self, stmt: dict[str, Any]) -> str | None:
+        """Emit an if statement with static (non-reactive) rendering."""
         # Generate unique labels for this if statement
         if_id = self._new_var()
         then_label = f"if.then.{if_id}"