feat: include lastExecutionError in useNodeErrorFlagSync reconciliation

## Summary

In `src/composables/graph/useNodeErrorFlagSync.ts`, the `reconcileNodeErrorFlags` function currently only consumes `lastNodeErrors` (validation errors), missing-model IDs, and missing-media IDs. Runtime errors stored in `lastExecutionError` (populated by `processExecutionError()`) are never fed into this reconciliation path, which means `has_errors` can be cleared on the canvas for a node that has a visible runtime failure in the Errors tab.

## Background

This was identified during review of PR #10309. The design decision to keep them separate was intentional — `lastExecutionError` has different lifecycle semantics (persists until next execution) versus `lastNodeErrors` (cleared on graph reload). Adding it to the reconciliation requires careful handling of clear-vs-retain timing.

## Proposed Follow-up

- Investigate the correct timing semantics for integrating `lastExecutionError` into `reconcileNodeErrorFlags`
- Ensure that clearing `lastExecutionError` (e.g., on new execution start) also triggers reconciliation so `has_errors` is cleared on the canvas accordingly
- Verify that the fix is applied consistently across both OSS and cloud pipelines

## References

- PR: https://github.com/Comfy-Org/ComfyUI_frontend/pull/10309
- Review comment: https://github.com/Comfy-Org/ComfyUI_frontend/pull/10309#discussion_r2960142214
- Requested by: @jaeone94

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