feat: comment categories; emend, relink and resolve corrections

scienting-layer/1: an optional, fixed category on comment, caveat and
question bodies (comment, context, critique, question, correction,
feedback, resource).

Corrections: emend fixes the authors' own slip and keeps what was printed
(a run's printed), never lowering fidelity or a witness match; relink sets
or removes what a citation names; resolve sets a reference's resolution.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017R7sgDNvUGWY2zFPCq2JH6

schemas/annotation.schema.json

@@ -3,6 +3,20 @@
   "$id": "https://paperspec.scient.ing/schemas/annotation.schema.json",
   "title": "Annotation",
   "description": "One line of annotations.jsonl in scienting-layer/1: a W3C Web Annotation; spec/18-layers.md.",
+  "$defs": {
+    "category": {
+      "description": "What a comment, caveat or question is about (spec/18 §18.4).",
+      "enum": [
+        "comment",
+        "context",
+        "critique",
+        "question",
+        "correction",
+        "feedback",
+        "resource"
+      ]
+    }
+  },
   "type": "object",
   "properties": {
     "@context": {
@@ -173,6 +187,9 @@
             },
             "kind": {
               "const": "comment"
+            },
+            "category": {
+              "$ref": "#/$defs/category"
             }
           },
           "required": [
@@ -203,6 +220,9 @@
             },
             "kind": {
               "const": "caveat"
+            },
+            "category": {
+              "$ref": "#/$defs/category"
             }
           },
           "required": [
@@ -240,6 +260,9 @@
                 "group",
                 "authors"
               ]
+            },
+            "category": {
+              "$ref": "#/$defs/category"
             }
           },
           "required": [