grammar: promote editor-note channel marker to named node

Editor notes have two semantic channels in original SiSU markup:

  ~[* ... ]~   asterisk set, general annotations (e.g. on the author)
  ~[+ ... ]~   plus set, a separate channel (e.g. TODO / review)

These are not interchangeable - the channel is meaningful, and
themes should be free to colour them differently. Promote the
opener from an inline literal to a named child node
(editor_note_marker) on a `marker:` field, and give it the
@attribute capture in highlights.scm - distinct from the generic
@punctuation.special used for ~{ / }~ / ]~.

A bare `~[ ... ]~` without `*` or `+` is intentionally rejected:
authors must pick a channel. This surfaces the markup bug at
/Not Without Help/ line 695 (which uses the bare form) as a parse
error, consistent with the project rule that strict structural
parsing is preferred over silent regex permissiveness.

Test corpus updated to expect the new (editor_note_marker) child.

(assisted by Claude-Code)

1 files changed, 16 insertions, 9 deletions

diff --git a/src/node-types.json b/src/node-types.json
index 48b593d..23a8908 100644
--- a/src/node-types.json
+++ b/src/node-types.json
@@ -451,7 +451,18 @@
   {
     "type": "editor_note",
     "named": true,
-    "fields": {},
+    "fields": {
+      "marker": {
+        "multiple": false,
+        "required": true,
+        "types": [
+          {
+            "type": "editor_note_marker",
+            "named": true
+          }
+        ]
+      }
+    },
     "children": {
       "multiple": true,
       "required": false,
@@ -1936,6 +1947,10 @@
     "named": true
   },
   {
+    "type": "editor_note_marker",
+    "named": true
+  },
+  {
     "type": "footnote_marker",
     "named": true
   },
@@ -2092,14 +2107,6 @@
     "named": false
   },
   {
-    "type": "~[*",
-    "named": false
-  },
-  {
-    "type": "~[+",
-    "named": false
-  },
-  {
     "type": "~{",
     "named": false
   }