On failed subgraph resolution, return undefined (#6460)

Resolving an executionId to a locatorId can fail if the current workflow
does not match the queued one. Rather than throwing an error, the
resolution functions have been changed to return undefined.

Of note, all consumers of these functions already had checks to ensure
the returned value is not undefined.
- Even the test for failure state already specified that it should
return instead of throwing an error.

This PR cleans up a frequent sentry error.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-6460-On-failed-subgraph-resolution-return-undefined-29c6d73d365081c5860ed7d24a99414c)
by [Unito](https://www.unito.io)

tests-ui/tests/store/executionStore.test.ts

@@ -156,14 +156,11 @@ describe('useExecutionStore - NodeLocatorId conversions', () => {
       expect(result).toBe('123')
     })
 
-    it('should return null when conversion fails', () => {
+    it('should return undefined when conversion fails', () => {
       // Mock app.graph.getNodeById to return null (node not found)
       vi.mocked(app.graph.getNodeById).mockReturnValue(null)
 
-      // This should throw an error as the node is not found
-      expect(() => store.executionIdToNodeLocatorId('999:456')).toThrow(
-        'Subgraph not found: 999'
-      )
+      expect(store.executionIdToNodeLocatorId('999:456')).toBe(undefined)
     })
   })