[BHP1-1479] Unify app / server mode under behave.core/-main

[rjsheperd]

Purpose

Reworks the behave.core/-main to auto-detect when the application is
running under JAR-mode vs. Conveyor/Executable mode.

Related Issues

Closes BHP1-1479

Submission Checklist

• Included Jira issue in the PR title (e.g. BHP1-### <title>)
• Code passes linter rules (clj-kondo --lint components/**/src bases/**/src projects/**/src)
• Feature(s) work when compiled (clojure -M:compile-cljs)

Testing

1. Copy standalone config:
   cd projects/behave/resources && cp config.standalone.edn config.edn

2. Use bb build-js to build the static assets

3. Use bb uber to build the UberJar

4. Verify that you when you double-click the JAR file, Behave starts
   in server mode and your default browser opens

[Kcheung42]

The application isn't staring up for me. I see the java process start up and a folder ~/.behave is created with no contents.

[Kcheung42]

I also tried launching the jar from within my wsl enviornment java -jar. The application launches but got a blank page:

[rjsheperd]

@Kcheung42 Ah, please also use bb build-js before using bb uber