feat(automation): rename to arrange-selection and add distribution

[andypalmi]

Summary

• Rename automation/align-selection action to automation/arrange-selection to support both alignment and distribution
• Add horizontally and vertically distribution directions that invoke core:distribute-selection-horizontally/vertically
• Distribution requires at least 3 non-config nodes (Node-RED core requirement)
• Improved error message for invalid directions now lists valid options

This renames the action introduced in #347 (not yet released).

Test plan

• Verify horizontal distribution invokes the correct core action with 3+ nodes
• Verify vertical distribution invokes the correct core action with 3+ nodes
• Verify distribution with fewer than 3 nodes is rejected
• Verify all existing alignment directions still work under the new action name
• Verify invalid directions produce a descriptive error message

Closes #352

[Steve-Mcl]

ARRANGE_SELECTION infers it will operate on the selection however the schema expects the array of ids - this is unclear and confusing (to humans and AI). A better name might be simply arrange_nodes coupled with a parameter UseCurrentSelection? or the omittance of ids means work on the selection?

Do we want to split MCP tools into arrange_selection and arrange_nodes ?

Consider the conversation:
→ Select all the debug nodes
← Selected 3 debug nodes
→ Align them left and space vertically
← align ids 1,2,3 left
← vertically space ids 1,2,3

The AI will need to maintain the array of nodes to operate on & send them every time.

Consider the conversation:
→ user selects things to modify
→ Align the selection left and space vertically
← gets selected ids 1,2,3
← align ids 1,2,3 left
← vertically space ids 1,2,3

The AI still needs to maintain the array of nodes to operate on & send them every time.

By supporting arrange_selection this changes

Consider the conversation:
→ user selects things to modify
→ Align the selection left and space vertically
← align selection left
← vertically space selection

The AI simply issues the automation to perform the operations without maintaing a list of IDs or acidentally selecting wrong things