[Release Blocker] Dev UI broken on `main` branch (fine on v0.2.0 release)

[vorburger]

I've just noticed that the Dev UI is broken on the main branch on cb95b56 (but's it's fine on the last v0.2.0 release, of course).

Spring Boot cannot find the HTML of the Dev UI anymore, and shows the generic Spring error page; see also #301. (I've not investigated why.)

Noticed this in a project where I'm using the ADK that worked with 0.2.0 and when I switched to using "bleeding edge" main by using JitPack (with enola-dev/enola#1565) then it was broken.

This should probably be fixed before the next release. Perhaps a non-regression test for it would be useful as well.

@glaforge @Poggecci @shukladivyansh FYI

[vorburger]

Perhaps a non-regression test for it would be useful as well.

FYI this is what I'm using to detect future regressions in a project using ADK...

... perhaps we should have something like that in ADK itself.

[vorburger]

@Poggecci is going to have a closer look into this... Thank You!

[vorburger]

@Poggecci FYI enola-dev/enola#1600 is how I can (still, even with today's latest rev) repro this, in my project.

I'll now see if I can also repro it using a simpler basic ADK Java Quickstart like project.

While I'm at it, I'll also look into contributing test coverage for this (if needed).