fix: kits:install prompts if some configurations are missing (#11009)

* fix: kits:install prompts if some configurations are missing

* dont prompt for noninteractive=true & select from unconfiguredInstanceIds directly

* refactor(functions): address review comments on kit instance prompting and config checks

- Routes options.instanceId in addKitInstanceOrConfigureProject to properly support configuring existing unconfigured instances or creating net-new instances non-interactively.
- Renames isKitConfiguredForProject to isKitFullyConfiguredForProject, reuses getUnconfiguredInstancesForProject, and documents 0-instance behavior.
- Derives isConfiguredForProject in memory from unconfiguredInstances to avoid redundant disk reads.
- Clarifies error message when an instance ID does not exist in a kit.
- Types unconfiguredInstanceIds as readonly string[].
- Fixes ExistingFunctionsInfo mock types to use arrays following #11008.

* remove unused isKitFullyConfiguredForProject