[core] Put ComponentMarker outside the IIFE as a visual bracket

The marker comment was being emitted as the first line *inside* each
IIFE:

  []() {
    // === logger ===
    // logger:
    //   ...
    ...
  }();

That works but buries the component label inside the lambda body, so
scanning generated main.cpp to find "where does component X's setup
live" is harder than it needs to be. Emit the marker before and after
the IIFE instead:

  // === logger ===
  []() {
    // logger:
    //   ...
    ...
  }();
  // === logger ===

Comment-only components (e.g. sha256, async_tcp, empty platforms like
binary_sensor:) don't grow a useless trailing duplicate marker —
when there's no IIFE to bracket, the marker is emitted once.

tests/unit_tests/test_core.py

@@ -961,8 +961,23 @@ def test_cpp_main_section_component_marker_wraps_in_iife() -> None:
     out = target.cpp_main_section
     assert out.count("[]() {") == 2
     assert out.count("}();") == 2
-    assert "// === logger ===" in out
-    assert "// === wifi ===" in out
+    # Each component's marker brackets its IIFE (once before, once after).
+    assert out.count("// === logger ===") == 2
+    assert out.count("// === wifi ===") == 2
+
+
+def test_cpp_main_section_comment_only_component_emits_single_marker() -> None:
+    # A component that emits no C++ statements (only a ComponentMarker)
+    # should not grow a useless trailing duplicate marker.
+    target = core.EsphomeCore()
+    target.main_statements = [
+        ComponentMarker("sha256"),
+        ComponentMarker("wifi"),
+        RawStatement("new_wifi();"),
+    ]
+    out = target.cpp_main_section
+    assert out.count("// === sha256 ===") == 1
+    assert out.count("// === wifi ===") == 2  # wifi has an IIFE
 
 
 def test_cpp_main_section_prefix_statements_stay_outside_iife() -> None: