Show class hierarchy links in ontology panels

[ousamabenyounes]

Closes #510.

Summary

• Make every displayed parent class a link that selects and focuses that class.
• Add a Subclasses field with direct children as navigable links.
• Explain in the empty Relations tab that inheritance lives under Definition.
• Keep the English and Chinese interfaces aligned.

Test verification (RED → GREEN)

• RED: the new hierarchy-detail regression could not import the absent subclass capability, and the existing empty-state copy did not name Definition (issue-510-red.log).
• GREEN: the focused web suite passes with parent/direct-subclass rendering, click-handler assertions, leaf empty-state coverage, and both locale contracts (10 tests total).
• Fix-revert RED: restoring the old parent rendering and Relations copy makes the two behavior assertions fail (issue-510-fix-revert-red.log).
• Full local suite: migrations ran twice; formatting, workspace clippy, workspace tests, database-backed utopia-store tests, workspace build, web tests, and production web build passed. After rebasing onto current dev, the affected web suite and production build passed again.
• Changed-line coverage: every changed executable hierarchy branch is rendered; both navigation handlers are invoked and asserted; the leaf branch and all changed locale values are asserted.
• Delivery: task-owned Chromium sessions exercised the real /kb/<id>/ontology route against a real backend/database in both English and Chinese. The browser navigated child → parent → child → grandchild, focused the matching schema node, opened Relations, and verified the localized guidance.

Review

Two independent Codex reviews accepted the final rebased diff after the one-use subclass filter was inlined and real-route Chromium evidence was captured.