fix(core): deprecate camelCase targets aliases

[christso]

Closes #907

Summary

• warn on deprecated camelCase aliases in targets.yaml validation and target resolution
• keep existing aliases working while guiding users to snake_case keys
• avoid duplicate CLI eval warnings by suppressing resolver-side warning emission after validation

Verification

• bun test packages/core/test/evaluation/providers/targets.test.ts packages/core/test/evaluation/validation/targets-validator.test.ts
• bunx biome check packages/core/src/evaluation/providers/targets.ts packages/core/src/evaluation/providers/types.ts packages/core/src/evaluation/validation/targets-validator.ts apps/cli/src/commands/eval/targets.ts packages/core/test/evaluation/providers/targets.test.ts packages/core/test/evaluation/validation/targets-validator.test.ts

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