refactor: Deduplicate catmaid spatially indexed skeletons code

[afonsobspinto]

• Centralizes spatial skeleton edit action metadata in command_factories.ts, including the action-to-command-property mapping, required vs optional command support, and confidence-configuration requirements.
• Reuses that metadata for editable source validation, command factory lookup, UI support checks, and public command execution wrappers.
• Replaces repeated per-action execution logic with shared execution metadata for unsupported-action errors and pending status messages.
• Consolidates CATMAID spatial skeleton command helpers for created-node cache updates, delete/undo flows, positive segment ID normalization, and CATMAID model-space position validation.
• Moves shared CATMAID/client, skeleton metadata, and grid-level helpers into reusable modules used by both frontend and backend paths.
• Renames the CATMAID node-list client method to the generic fetchNodes.
• Removes the now-unused dedupeSpatiallyIndexedSkeletonEntries helper.
• Adds/updates tests around shared action routing, editable-source support detection, confidence editing support, and CATMAID API expectations.