Highlight telemetry rows when hovering a graph action

[HsbcJone]

Hovering an action in the graph view now highlights the matching rows in the telemetry UI, the reverse of the existing telemetry-to-graph hover.

Closes #275

Changes

• Graph hover is keyed by action name plus the application and partition that own the graph, because one action can run many times.
• Pointing at a node highlights every step, span, and insight line for that action, and the node uses the existing graph hover style.
• Hovering a telemetry row still highlights only that sequence. The two hover sources clear each other.
• Nested applications that reuse an action name do not highlight each other.

How I tested this

In telemetry/ui:

• npm ci
• npm run build (tsc and Vite)
• npm run lint
• npm run format
• npx vitest run (5 passed, including 4 new cases for the hover rule)

Notes

The earlier attempt on this issue had no pull request and the issue was unassigned, so this picks it up.

Checklist

• PR has an informative and human-readable title (this will be pulled into the release notes)
• Changes are limited to a single goal (no scope creep)
• Code passed the pre-commit check & code is left cleaner/nicer than when first encountered.
• Any change in functionality is tested
• New functions are documented (with a description, list of inputs, and expected output)
• Placeholder code is flagged / future TODOs are captured in comments
• Project documentation has been updated if adding/changing functionality.