Fix IdentifiedObject SHACL path subjects

[wenxiaojie1]

Summary

• Replace ?s $PATH ?value with $this $PATH ?value in the four IdentifiedObject SHACL string-length SPARQL constraints called out in the issue.
• Keep the query subject aligned with the selected $this focus node.

Validation

• Confirmed the four issue-referenced lines now use $this $PATH ?value.
• Ran git diff --check.

Note: I could not run a local Turtle parse because rdflib is not installed in this environment.

Closes #76