Fix Neo4j enum conversion: add NodeKind/EdgeKind converters for SDN

Spring Data Neo4j uses Enum.valueOf() by default, which expects uppercase
constant names (METHOD, CLASS). But Neo4j stores lowercase values (method,
class). Added @convertwith converters that map via fromValue()/getValue().

Fixes: IllegalArgumentException: No enum constant NodeKind.method

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: aksOps

src/main/java/io/github/randomcodespace/iq/model/CodeEdge.java

@@ -23,6 +23,7 @@ public class CodeEdge {
 
     private String id;
 
+    @ConvertWith(converter = EdgeKindConverter.class)
     private EdgeKind kind;
 
     private String sourceId;

src/main/java/io/github/randomcodespace/iq/model/CodeNode.java

@@ -23,6 +23,7 @@ public class CodeNode {
     @Id
     private String id;
 
+    @ConvertWith(converter = NodeKindConverter.class)
     private NodeKind kind;
 
     private String label;

src/main/java/io/github/randomcodespace/iq/model/EdgeKindConverter.java

@@ -0,0 +1,22 @@
+package io.github.randomcodespace.iq.model;
+
+import org.neo4j.driver.Value;
+import org.springframework.data.neo4j.core.convert.Neo4jPersistentPropertyConverter;
+
+/**
+ * Converts between EdgeKind enum and its lowercase string value for Neo4j storage.
+ * Neo4j stores "depends_on", "calls", etc. — not "DEPENDS_ON", "CALLS".
+ */
+public class EdgeKindConverter implements Neo4jPersistentPropertyConverter<EdgeKind> {
+
+    @Override
+    public Value write(EdgeKind kind) {
+        return org.neo4j.driver.Values.value(kind != null ? kind.getValue() : null);
+    }
+
+    @Override
+    public EdgeKind read(Value source) {
+        if (source == null || source.isNull()) return null;
+        return EdgeKind.fromValue(source.asString());
+    }
+}

src/main/java/io/github/randomcodespace/iq/model/NodeKindConverter.java

@@ -0,0 +1,22 @@
+package io.github.randomcodespace.iq.model;
+
+import org.neo4j.driver.Value;
+import org.springframework.data.neo4j.core.convert.Neo4jPersistentPropertyConverter;
+
+/**
+ * Converts between NodeKind enum and its lowercase string value for Neo4j storage.
+ * Neo4j stores "method", "class", etc. — not "METHOD", "CLASS".
+ */
+public class NodeKindConverter implements Neo4jPersistentPropertyConverter<NodeKind> {
+
+    @Override
+    public Value write(NodeKind kind) {
+        return org.neo4j.driver.Values.value(kind != null ? kind.getValue() : null);
+    }
+
+    @Override
+    public NodeKind read(Value source) {
+        if (source == null || source.isNull()) return null;
+        return NodeKind.fromValue(source.asString());
+    }
+}