Add tooltips and refine clickable schema type affordances

[kmcginnes]

Description

Follow-up polish on the clickable node/edge types in the Schema Explorer details panel (shipped in #1731). Makes the click affordance discoverable and explains what it does:

• Tooltip on hover or keyboard focus — each clickable type shows "Change selection to {label}" so users know activating it re-selects that type (and highlights it in the graph).
• Clearer at-rest affordance — clickable types get a hover background tint and color shift; the focus ring now matches the rest of the codebase (ring-ring-3 / outline-hidden).
• The currently-selected type is intentionally not clickable — it renders as a plain label with no tooltip, since re-selecting it would be a no-op.
• Accessibility — the decorative → arrow separators are now aria-hidden siblings, so each type button's accessible name is just its label (e.g. "knows", not "→ knows →").

Supporting refactor (no behavior change): extracted a shared ClickableTypeText primitive to remove the duplicated button-vs-span branches, and a toSelectedElements helper alongside the existing toSchemaGraphSelection so both selection-mapping directions live together.

How to read

1. Details.tsx — start here; the ClickableTypeText primitive, tooltip, hover/focus styling, selected-type span, and aria-hidden separators
2. SchemaGraph.tsx — the extracted toSelectedElements helper next to toSchemaGraphSelection
3. Details.test.tsx — behavior coverage for the clickable/selected/tooltip/accessible-name cases
4. toSchemaGraphSelection.test.ts — mapping tests for toSelectedElements

Validation

• node_modules/.bin/vitest run packages/graph-explorer/src/modules/SchemaGraph — 22 tests pass, including new coverage for the selected-type-not-clickable behavior, the clean accessible name, the focus tooltip, and the toSelectedElements mapping.
• tsc --noEmit, oxlint, and oxfmt --check clean on the changed files.

Related Issues

• Related to Add clickable links for node types and edge types in schema explorer details panel #1731
• Related to Add clickable links for node types and edge types in schema explorer details panel #1542

Check List

• I confirm that my contribution is made under the terms of the Apache 2.0 license.
• I have verified pnpm checks passes with no errors.
• I have verified pnpm test passes with no failures.
• I have covered new added functionality with unit tests if necessary.
• I have updated documentation if necessary.