Add optional direction arrows for graph links

[CAJazzer]

Summary

Adds an optional setting to display semantic direction arrows on Graph Link Types edges.

This helps relationships such as:

architecture for:: [[My Product]]
A product of:: [[My Company]]

render visually as directed relationships in the graph.

Added behavior

• Adds a Show Direction setting.
• Default behavior draws one arrow from the source note to the target note.
• Supports per-link overrides:
  • relationship__none:: [[Target]] hides arrows for that link.
  • relationship__both:: [[Target]] displays arrows in both directions.
• Cleans display labels so sibling to__both renders as sibling to.

Why

Typed link labels are useful, but without direction, relationships like works for, architecture for, or product of can be visually ambiguous in graph view.

Notes

The feature is disabled by default and should preserve existing behavior unless enabled.