fb5a1988b1
## Summary
When a workspace migration action fails during workspace iteration (e.g.
during upgrade commands), only the wrapper message was logged:
```
[WorkspaceIteratorService] Error in workspace 7914ba64-...: Migration action 'create' for 'pageLayoutWidget' failed
```
The underlying error (transpilation/metadata/workspace schema) and its
stack were swallowed, making production debugging painful.
This PR adds a follow-up log entry for each inner error attached to a
`WorkspaceMigrationRunnerException`, including its message and stack
trace. The runner exception itself is untouched — it already exposes
structured `errors` (`actionTranspilation`, `metadata`,
`workspaceSchema`).
After this change, logs look like:
```
[WorkspaceIteratorService] Error in workspace 7914ba64-...: Migration action 'create' for 'pageLayoutWidget' failed
[WorkspaceIteratorService] Caused by actionTranspilation in workspace 7914ba64-...: <real reason>
at ...
```
## Test plan
- [ ] Trigger a failing workspace migration (e.g. backfill record page
layouts) on a workspace and confirm the underlying cause + stack now
appear in logs.
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