fix(cli): remove promptfoo import support - #1552

Summary

AgentV no longer advertises or accepts Promptfoo config import as a supported core path. The import command is scoped back to transcript and dataset imports, while the public docs direct Promptfoo users toward native AgentV eval YAML or external one-off migration tooling.

This removes the Promptfoo converter implementation and its importer tests, unregisters agentv import promptfoo, and adds CLI coverage that the removed subcommand stays out of import help and is rejected when invoked.

Validation

• bun install
• bun run build
• bun test apps/cli/test/eval.integration.test.ts -t "promptfoo|non-eval dry-run"
• bun apps/cli/src/cli.ts import --help
• bun apps/cli/src/cli.ts import promptfoo
• bun run typecheck
• bun run lint
• git diff --check
• bun --filter @agentv/web build
• Manual review: remaining Promptfoo mentions are historical research, prior-art/attribution, industry-practice comments, or the explicit import deprecation note.

Post-Deploy Monitoring & Validation

No additional production monitoring is required because this removes a local CLI/docs surface and does not change a running service.

• Watch: GitHub Actions CI for typecheck, lint, tests, docs build, and package build on this PR.
• Healthy signals: agentv import --help omits promptfoo; agentv import promptfoo rejects the subcommand; /docs/tools/import/ builds and no longer presents Promptfoo import as supported.
• Failure signals: CI failures in CLI help tests, docs build, or package typecheck; reports that the removed command still appears in generated help/docs.
• Mitigation: revert 5b09fd70 or restore only the missing docs/test wiring if CI identifies a narrower regression.
• Validation window and owner: PR author through merge.