refactor: Restructure main with cmd/app structure

[raeperd]

Issue to fix

• root level main package force project structure, which is not preferable

solved with

• main.go -> cmd/app/main.go
• api/openapi.yaml -> cmd/app/openapi.yaml
• Makefile build target with -trimpath

[raeperd]

@SeaRoll
This pr is still in draft means not ready to be reviewed yet.

[SeaRoll]

Just commenting for some insight later on 👀 looked cool otherwise

[raeperd]

After reviewing the structure, I've decided not to merge this PR at this time, as I'm uncertain if it aligns with the project's current direction. However, it's possible that we might revisit this in the future. Please feel free to stay engaged and contribute further.