feat(02-02): add ELK/JFreeSVG dependencies and core diagram rendering interfaces

- Add Eclipse ELK core + layered algorithm and JFreeSVG dependencies to app module
- Create DiagramRenderer interface in core with renderSvg and layoutJson methods
- Create DiagramLayout, PositionedNode, PositionedEdge records for layout data

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

cameleer3-server-app/pom.xml

@@ -46,6 +46,21 @@
             <artifactId>springdoc-openapi-starter-webmvc-ui</artifactId>
             <version>2.8.6</version>
         </dependency>
+        <dependency>
+            <groupId>org.eclipse.elk</groupId>
+            <artifactId>org.eclipse.elk.core</artifactId>
+            <version>0.11.0</version>
+        </dependency>
+        <dependency>
+            <groupId>org.eclipse.elk</groupId>
+            <artifactId>org.eclipse.elk.alg.layered</artifactId>
+            <version>0.11.0</version>
+        </dependency>
+        <dependency>
+            <groupId>org.jfree</groupId>
+            <artifactId>org.jfree.svg</artifactId>
+            <version>5.0.7</version>
+        </dependency>
         <dependency>
             <groupId>org.springframework.boot</groupId>
             <artifactId>spring-boot-starter-test</artifactId>

cameleer3-server-core/src/main/java/com/cameleer3/server/core/diagram/DiagramLayout.java

@@ -0,0 +1,21 @@
+package com.cameleer3.server.core.diagram;
+
+import java.util.List;
+
+/**
+ * Complete diagram layout with positioned nodes and edges.
+ * <p>
+ * This is the JSON response format for the layout endpoint.
+ *
+ * @param width  total diagram width
+ * @param height total diagram height
+ * @param nodes  positioned nodes with coordinates
+ * @param edges  positioned edges with waypoints
+ */
+public record DiagramLayout(
+        double width,
+        double height,
+        List<PositionedNode> nodes,
+        List<PositionedEdge> edges
+) {
+}

cameleer3-server-core/src/main/java/com/cameleer3/server/core/diagram/DiagramRenderer.java

@@ -0,0 +1,28 @@
+package com.cameleer3.server.core.diagram;
+
+import com.cameleer3.common.graph.RouteGraph;
+
+/**
+ * Renders route diagrams from {@link RouteGraph} definitions.
+ * <p>
+ * Implementations produce either SVG documents for direct display or
+ * JSON-serializable layout data for client-side rendering.
+ */
+public interface DiagramRenderer {
+
+    /**
+     * Render the route graph as an SVG XML document.
+     *
+     * @param graph the route graph definition
+     * @return SVG XML string
+     */
+    String renderSvg(RouteGraph graph);
+
+    /**
+     * Compute the diagram layout with positioned nodes and edges.
+     *
+     * @param graph the route graph definition
+     * @return layout data suitable for JSON serialization
+     */
+    DiagramLayout layoutJson(RouteGraph graph);
+}

cameleer3-server-core/src/main/java/com/cameleer3/server/core/diagram/PositionedEdge.java

@@ -0,0 +1,19 @@
+package com.cameleer3.server.core.diagram;
+
+import java.util.List;
+
+/**
+ * An edge with computed waypoints for rendering.
+ *
+ * @param sourceId source node identifier
+ * @param targetId target node identifier
+ * @param label    optional edge label
+ * @param points   list of [x, y] waypoints from source to target
+ */
+public record PositionedEdge(
+        String sourceId,
+        String targetId,
+        String label,
+        List<double[]> points
+) {
+}

cameleer3-server-core/src/main/java/com/cameleer3/server/core/diagram/PositionedNode.java

@@ -0,0 +1,30 @@
+package com.cameleer3.server.core.diagram;
+
+import java.util.List;
+
+/**
+ * A node with computed layout position and dimensions.
+ * <p>
+ * For compound nodes (CHOICE, SPLIT, TRY_CATCH, etc.), {@code children}
+ * contains the nested child nodes rendered inside the parent bounds.
+ *
+ * @param id       node identifier (matches RouteNode.id)
+ * @param label    display label
+ * @param type     NodeType name (e.g., "ENDPOINT", "PROCESSOR")
+ * @param x        horizontal position
+ * @param y        vertical position
+ * @param width    node width
+ * @param height   node height
+ * @param children nested child nodes for compound/swimlane groups
+ */
+public record PositionedNode(
+        String id,
+        String label,
+        String type,
+        double x,
+        double y,
+        double width,
+        double height,
+        List<PositionedNode> children
+) {
+}