Fix SkipPrefix dropping value field in KeyValue nodes (#4478)

## Changes

The SkipPrefix method was not copying the value field when creating new
PathNodes, causing KeyValue nodes (e.g., `[task_key='my_task']`) to lose
their value part. This would corrupt paths containing KeyValue nodes
after calling SkipPrefix.

## Tests
Unit tests.

Co-authored-by: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: denik

libs/structs/structpath/path.go

@@ -614,6 +614,7 @@ func (p *PathNode) SkipPrefix(n int) *PathNode {
 			prev:  result,
 			key:   current.key,
 			index: current.index,
+			value: current.value,
 		}
 		current = current.Parent()
 	}

libs/structs/structpath/path_test.go

@@ -551,6 +551,38 @@ func TestPrefixAndSkipPrefix(t *testing.T) {
 			prefix:     "",
 			skipPrefix: "resources.jobs.my_job.tasks[0].name",
 		},
+		// Regression test for SkipPrefix bug: value field was missing in KeyValue nodes
+		// Test all possible n values for completeness
+		{
+			input:      "resources.jobs[task_key='my_task'].notebook_task",
+			n:          0,
+			prefix:     "",
+			skipPrefix: "resources.jobs[task_key='my_task'].notebook_task",
+		},
+		{
+			input:      "resources.jobs[task_key='my_task'].notebook_task",
+			n:          1,
+			prefix:     "resources",
+			skipPrefix: "jobs[task_key='my_task'].notebook_task",
+		},
+		{
+			input:      "resources.jobs[task_key='my_task'].notebook_task",
+			n:          2,
+			prefix:     "resources.jobs",
+			skipPrefix: "[task_key='my_task'].notebook_task",
+		},
+		{
+			input:      "resources.jobs[task_key='my_task'].notebook_task",
+			n:          3,
+			prefix:     "resources.jobs[task_key='my_task']",
+			skipPrefix: "notebook_task",
+		},
+		{
+			input:      "resources.jobs[task_key='my_task'].notebook_task",
+			n:          4,
+			prefix:     "resources.jobs[task_key='my_task'].notebook_task",
+			skipPrefix: "",
+		},
 	}
 
 	for _, tt := range tests {