Add base system groups

[waynemwashuma]

Objective

Introduce built-in core scheduling phases by adding reusable core system groups for startup and update schedules while making App#createSchedule() chainable.

Solution

Previously, startup and update schedules were created independently without predefined execution phases. This privides systems with a way to be ordered in larger base groups that are defined by the engine.

Changes include:

• Added built-in core system groups:
  • Start
  • PreMain
  • Main
  • PostMain
  • End

Core execution flow:

flowchart LR
    Start --> PreMain --> Main --> PostMain --> End

Loading

The scheduling phases provide a consistent execution structure across applications while still allowing custom ordering and extension through existing group APIs.

Returning the app instance from createSchedule() aligns it with the rest of the fluent application configuration API and simplifies plugin setup code.Systems can now automatically participate in the default Main phase if registered without a system group in the core schedules.

Showcase

N/A

Migration guide

No migrations required

Notes

• Systems without an explicit group now default to CoreSystems.Main inside core schedules
• Existing explicit system groups continue to work unchanged

Checklist

• I have updated the documentation accordingly.
• I have added tests to cover my changes.