Revert "sessions - improve session hover title rendering and persistence"

[bpasero]

Reverts #298950

[Copilot]

Pull request overview

This PR reverts #298950, which had introduced improvements to session hover title rendering (using renderAsPlaintext on the markdown label for a simple hover) and persistence. The revert rolls back the rename from disableHover → useSimpleHover and removes the plaintext hover rendering that was added in that PR, restoring the original early-return behavior when hover is disabled.

Changes:

• Renames the option useSimpleHover back to disableHover in all relevant interfaces and usages.
• Removes the plaintext-markdown hover rendering logic that was introduced in #298950, restoring the simple early-return when hover is disabled.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
agentSessionsViewer.ts	Reverts IAgentSessionRendererOptions.useSimpleHover → disableHover; restores renderHover to return early instead of showing a plaintext hover
agentSessionsControl.ts	Reverts IAgentSessionsControlOptions.useSimpleHover → disableHover
sessionsViewPane.ts	Reverts usage site: useSimpleHover: true → disableHover: true
agentSessionsViewer.fixture.ts	Reverts test fixture: useSimpleHover: true → disableHover: true