feat(experiments): support suite test selectors

[christso]

Summary

• add canonical experiment suites[] entries with suite-local select.test_ids[] selectors
• resolve selected suite tests into experiment run metadata and CLI execution
• update schemas, docs, examples, and eval-builder guidance to use suites/test_ids only
• hard-remove prerelease experiment evals surface without compatibility messaging

Verification

• bun test ./test/evaluation/experiment.test.ts ./test/evaluation/validation/eval-schema-sync.test.ts (packages/core)
• bunx biome check packages/core/src/evaluation/experiment.ts packages/core/test/evaluation/experiment.test.ts apps/web/src/content/docs/docs/evaluation/experiments.mdx
• earlier on this branch: bun test apps/cli/test/eval.integration.test.ts -t "runs a native experiment file with suite test selection and run knobs"
• earlier on this branch: bun run validate:examples
• earlier on this branch: bun --filter agentv typecheck