fix(edit_asset): converge attribute set into one self-healing op

[bobby-smedley]

🎯 What does this PR do?

What

set_attribute replaces update_attribute for normal single-valued attributes — it creates the value if absent, updates it if present. add_attribute is now scoped to appending values to multi-valued attributes. update_attribute stays as a silent, unadvertised back-compat alias.

Why

The agent had to choose add vs update without knowing whether the attribute already had a value, so it guessed wrong about half the time — failing the first call with an error, then retrying. chip already fetches the asset's attributes, so set_attribute decides create-vs-patch from state it already has: one call, correct regardless of which tool the agent picks.

Tests

• Unit: set creates when absent / patches when present (+ existing suite green).
• Live: bulk create, bulk patch, update_attribute alias, and mixed create+patch in one call — all single-call, no duplicates.

✅ Checklist

My code follows the style guidelines of this project.
I have performed a self-review of my own code.
I have commented my code, particularly in hard-to-understand areas.
I have made corresponding changes to the documentation (if needed).
My commit messages follow the Conventional Commits standard.

🤖 Generated with Claude Code