Move evaluator and assigner to shared package

[williamgrosset]

Summary

• Moves evaluateTargetingRules and assignVariants from decision-service/src/services/ into @experiments/shared, so both the decision-service and the upcoming client-side React SDK can import rule evaluation and variant assignment from a single source of truth.
• Updates the decision-service to import assignVariants from @experiments/shared instead of its local copy.
• Relocates the corresponding unit tests (evaluator.test.ts, assigner.test.ts) to packages/shared/test/.

Changes

File	Change
packages/shared/src/evaluator.ts	Moved from decision-service (import paths updated to local shared types)
packages/shared/src/assigner.ts	Moved from decision-service (imports evaluateTargetingRules locally, getBucket and types from shared)
packages/shared/src/index.ts	Exports evaluateTargetingRules and assignVariants
packages/shared/test/evaluator.test.ts	Moved from decision-service/test/ (import paths updated)
packages/shared/test/assigner.test.ts	Moved from decision-service/test/ (import paths updated)
decision-service/src/routes/decide.ts	Imports assignVariants from @experiments/shared instead of local ../services/assigner.js
decision-service/package.json	Adds --passWithNoTests flag since all tests moved to shared

Verification

• All 24 shared package unit tests pass (13 evaluator + 9 assigner + 2 hashing)
• All 10 experiment-service unit tests pass
• Build succeeds across all packages (shared, api-gateway, decision-service, experiment-service, dashboard)
• Zero logic changes — code was moved verbatim with only import path adjustments