Agents: Update session list styles and behavior

[hawkticehurst]

Fixes #317698
Fixes #317694

Update several parts of session list styling and behavior:

1. Stop using all caps for workspace title
2. Remove the 'selected' state from workspace titles
3. Instead of showing a background fill color when hovering over workspace title, the title text color is set to be the intense foreground variant
4. Show a chevron icon on hover to reinforce expanded/collapsed states of a workspace in the session list
5. Update "+N WORKSPACES" / "SHOW FEWER WORKSPACES" button/toggle so the text is left aligned, the text now says "+N more workspaces", and the text is no longer uppercase

[Copilot]

Pull request overview

This PR enhances the Agents window Sessions list section headers by adding a dedicated chevron element that reflects a section’s collapsed/expanded state, and wires collapse-state updates so the chevron stays in sync as users toggle sections.

Changes:

• Add a session-section-chevron element to section header templates and update its icon based on collapsed state.
• Forward tree collapse-state changes to the section renderer to keep the chevron updated without requiring a full renderElement pass.
• Update Sessions list CSS to style and show the chevron (and adjust hover/focus visuals for section rows).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
src/vs/sessions/contrib/sessions/browser/views/sessionsList.ts	Adds chevron element + renderer logic to keep the chevron state in sync with section collapse/expand.
src/vs/sessions/contrib/sessions/browser/media/sessionsList.css	Styles the new chevron and adjusts section-row hover/focus presentation.

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.