Address spec gaps identified from cdx-pandoc analysis

- Add semantic.schema.json for validating semantic extension blocks/marks
- Extend citation mark with CSL-compatible fields (prefix, suffix, locator, suppressAuthor)
- Add source field to entity mark for knowledge graph origin
- Add creators field to Dublin Core for structured author data with ORCID
- Document bibliography block inline entries with renderedText support
- Clarify linebreak semantics (soft breaks vs hard breaks)
- Document tableCell simplified form for text node children
- Document core vs semantic measurement type relationship
- Update CI workflow to validate semantic schema

Author: gvonness-apolitical

.github/workflows/validate-schemas.yml

@@ -31,7 +31,8 @@ jobs:
           for f in schemas/anchor.schema.json schemas/asset-index.schema.json \
                    schemas/content.schema.json schemas/dublin-core.schema.json \
                    schemas/manifest.schema.json schemas/precise-layout.schema.json \
-                   schemas/presentation.schema.json schemas/provenance.schema.json; do
+                   schemas/presentation.schema.json schemas/provenance.schema.json \
+                   schemas/semantic.schema.json; do
             echo "Compiling $f..."
             ajv compile -s "$f" --spec=draft2020 --strict=false
           done

schemas/dublin-core.schema.json

@@ -25,7 +25,13 @@
             { "type": "string", "minLength": 1 },
             { "type": "array", "items": { "type": "string" }, "minItems": 1 }
           ],
-          "description": "Primary author(s)"
+          "description": "Primary author(s) - simple string names for Dublin Core compatibility"
+        },
+        "creators": {
+          "type": "array",
+          "description": "Structured author data with ORCID and affiliation support",
+          "items": { "$ref": "#/$defs/creatorObject" },
+          "minItems": 1
         },
         "subject": {
           "oneOf": [
@@ -126,6 +132,32 @@
           "description": "License URL"
         }
       }
+    },
+    "creatorObject": {
+      "type": "object",
+      "description": "Structured creator/author information",
+      "required": ["name"],
+      "properties": {
+        "name": {
+          "type": "string",
+          "description": "Full name of the creator",
+          "minLength": 1
+        },
+        "orcid": {
+          "type": "string",
+          "description": "ORCID identifier (e.g., '0000-0001-2345-6789')",
+          "pattern": "^[0-9]{4}-[0-9]{4}-[0-9]{4}-[0-9]{3}[0-9X]$"
+        },
+        "affiliation": {
+          "type": "string",
+          "description": "Institutional affiliation"
+        },
+        "email": {
+          "type": "string",
+          "format": "email",
+          "description": "Contact email address"
+        }
+      }
     }
   }
 }