Hide 'Continue in...' menu when no delegation targets available

[Copilot]

The "Continue in..." menu was visible even when both background and cloud delegation targets were unavailable, showing non-functional setup buttons.

Changes

• Added context key hasContinueInOptions to track availability of Background/Cloud providers with canDelegate !== false
• Updated menu precondition to include the new context key, hiding the menu when no delegation targets exist
• Context key updates trigger on contribution registration and availability changes via _evaluateAvailability()

The menu now only appears when at least one delegation target (Background or Cloud) is actually available to users.

Original prompt

When both background and cloud are disabled (not available), the 'continue in ' menu still shows but its buttons do not work. We should hide all isntsances of the 'continue in...' menu when there is notihing registered to put in the menu!

Created from VS Code.

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.