feat(validator): detect broken/malformed workflow connections (#620)

Add comprehensive connection validation: unknown output keys with fix
suggestions, invalid type field detection, output/input index bounds
checking, and BFS-based trigger reachability analysis replacing simple
orphan detection.

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

dist/services/workflow-validator.d.ts

@@ -21,17 +21,7 @@ interface WorkflowNode {
 }
 interface WorkflowConnection {
     [sourceNode: string]: {
-        main?: Array<Array<{
-            node: string;
-            type: string;
-            index: number;
-        }>>;
-        error?: Array<Array<{
-            node: string;
-            type: string;
-            index: number;
-        }>>;
-        ai_tool?: Array<Array<{
+        [outputType: string]: Array<Array<{
             node: string;
             type: string;
             index: number;
@@ -94,6 +84,10 @@ export declare class WorkflowValidator {
     private validateErrorOutputConfiguration;
     private validateAIToolConnection;
     private validateAIToolSource;
+    private validateOutputIndexBounds;
+    private validateInputIndexBounds;
+    private flagOrphanedNodes;
+    private validateTriggerReachability;
     private hasCycle;
     private validateExpressions;
     private countExpressionsInObject;