Copilot instructions update

[BurningAXE]

Notable changes

• Used Opus 4.6 to analyze the project and generate instructions for itself
• I only did a few minor corrections and additions
• Then prompted it to add info about our event system, too

Additional work checklist

• Effect on other features and security has been considered
• Design document marked as "In development" (if applicable)
• External (Gitbook) and internal (Confluence) Documentation is up to date (or ticket created)
• Test cases in Testiny are up to date (or ticket created)
• Other teams notified about the changes (if applicable)

[luhmirin-s]

IIRC, the general instructions file is prepended to each prompt that we do in the repository, therefore it should be as short and generic as possible. IMO, there is a significant amount of redundant information and implementation details that could be cut-out from this version.

Also I am not convinced that every prompt needs a detailed explanation of the event system. Can it be in a separate prompt file and linked only when actually necessary?