Per qodo-ai-reviewer feedback on PR #44: Accessibility.getFullAXTree
was emitting AXNode.role as a plain string and name/value as plain
strings or null, instead of CDP-compliant AXValue objects.
Changes:
- Add ax_value_role() and ax_value_string() helpers
- Change compute_name()/compute_value() to return Option<String>
- Wrap role, name, value as AXValue in build_ax_node()
The properties array already used the correct AXValue format.