Fuzz Introspector status UI

There are projects like systemd where the full FI doesn't work upstream because of the way they are built and it causes issues like https://github.com/google/oss-fuzz/issues/12959 (where the status was successful with no FI reports). The light version of FI was added recently in https://github.com/google/oss-fuzz/pull/12983 and as far as I understand the status is shared currently. I think it would be great if it was a bit more intuitive to avoid confusion. It was discussed in https://github.com/google/oss-fuzz/pull/12983#issuecomment-2614452783 and filed here so that it wouldn't get lost.

Review the status behavior described in issue 12959 and the light Fuzz Introspector change in pull request 12983, including the linked discussion. Define how the UI should distinguish full and light FI outcomes, then verify that successful builds without FI reports are no longer presented ambiguously.

Written by the indexing model from the issue text.