fix: Resolve main entry path relative to project directory

[codekeyz]

This fixes issue for mono-repos where Globe CLI is run from root directory, but project directory isn't root directory.

serverpod_project 
  - serverpod_client
  - serverpod_flutter
  - serverpod_server (actual project directory)

Resolving main entry should return bin/main.dart instead of serverpod_server/bin/main.dart since serverpod_server is already our working directory.