sessions: refactor title bar to use sessions management service and add sessions picker command (#306053)

* refactor: streamline session management in SessionsTitleBarWidget and add Show Sessions Picker action

* feat: add Show Sessions Picker action and refactor session actions

* feat: enhance session visibility by including active session in filtered list

* fix: ensure active session is included in filtered list by matching sessionId

* fix: use sessionId instead of URI toString for picked state comparison

Co-authored-by: Copilot <[email protected]>

* refactor: reuse SessionItemContextMenuId for title bar context menu

Use the same menu ID and context key overlays as the sessions list
view instead of hardcoding actions, ensuring consistency.

Co-authored-by: Copilot <[email protected]>

---------

Co-authored-by: Copilot <[email protected]>