Implements the "Run selected nodes" feature (PR #61) with fixes for all 8
review issues: topological ordering via groupNodesByLevel, AbortController
cancellation, glbViewer case coverage, AbortError filtering, downstream
consumer propagation with dedup guard, and dynamic button label. Also
extracts saveLogSession helper to replace 4 inline duplicates across
executeWorkflow and regenerateNode.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
shrimbly