move assistant and webapp build-depends into main build-depends

move assistant and webapp build-depends into main build-depends

For some reason, cabal 3.4.1.0 builds w/o the assistant and webapp,
even when the flag is explicitly turned on. Moving the build-depends from
inside the if flag section to the main build-depends somehow fixes this.

Since the webapp build deps are thus always available, there is no reason
not to build the webapp when building the assistant. So, got rid of the
webapp build flag. Kept the assistant build flag for now, since building
without it does at least still speed up the build.

Sponsored-by: Brock Spratlen on Patreon