Forbid modules importing from core

Editor assessment

The subject states the rule and its direction exactly — modules are forbidden from importing from core — so the header communicates the lint policy and the dependency boundary it enforces without the diff, and chore(eslint) classifies the rule addition correctly. Hygiene is clean: imperative mood, no trailing period, sensible length, no ticket junk. The co-author trailer is well formed. No body is needed for a contained policy addition, and no footer is required. A line on the layering violation it prevents would add polish; the message is clear and publishable.