Move effect handlers from effects/ subdirectory to flat structure:
- effects/handlers.ts → effect.handlers.ts
- effects/registry.ts → effect.registry.ts
- effects/types.ts → effect.types.ts
Update import path in inventory.service.ts from
'@/modules/inventory/effects/registry' to
'@/modules/inventory/effect.registry'.
This reduces directory nesting and follows the convention of
keeping module files flat unless there are 5+ files.
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