feat: add interactive ProcessDiagram SVG component (sub-project 1/3)

New interactive route diagram component with SVG rendering using
server-computed ELK layout coordinates. TIBCO BW5-inspired top-bar
card node style with zoom/pan, hover toolbars, config badges, and
error handler sections below the main flow.

Backend: add direction query parameter (LR/TB) to diagram render
endpoints, defaulting to left-to-right layout.

Frontend: 14-file ProcessDiagram component in ui/src/components/
with DiagramNode, CompoundNode, DiagramEdge, ConfigBadge, NodeToolbar,
ErrorSection, ZoomControls, and supporting hooks. Dev test page at
/dev/diagram for validation.

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

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

@@ -19,4 +19,14 @@ public interface DiagramRenderer {
      * Compute a positioned JSON layout for the route graph.
      */
     DiagramLayout layoutJson(RouteGraph graph);
+
+    /**
+     * Compute a positioned JSON layout with a specific flow direction.
+     *
+     * @param graph     the route graph
+     * @param direction "LR" for left-to-right, "TB" for top-to-bottom
+     */
+    default DiagramLayout layoutJson(RouteGraph graph, String direction) {
+        return layoutJson(graph);
+    }
 }