Refactor namespaces to match new folder structure

[KotyaraDev]

What to do

Update all namespace declarations to correspond to the new directory structure.

Expected namespaces:

• SimpleZombieMode.Core for everything in core/
• SimpleZombieMode.Features.ZombieClasses for zombie classes
• SimpleZombieMode for main plugin files
• Update using statements everywhere

Acceptance criteria

• No more old namespaces (e.g. from src.services)
• Project builds without errors
• All classes are in correct namespaces

[KotyaraDev]

frozen until better times