test(e2e): move contract e2e to commands

[hopelynd]

Summary

Decouple E2E tests for the composable-cli architecture so command behavior and product entrypoints are tested separately.

• Move contract E2E to bailian-cli-commands: All help / dry-run / live-integration tests (27 files) now run against a canonical tests/fixtures/test-cli.ts entry (createCli(commands, …)), independent of bl or rag binaries.
• Add shared E2E harness under packages/commands/tests/e2e/core/: createCliRunner, skip helpers, output-dir utilities, and Vitest globalSetup (.env + session dir). Exposed as bailian-cli-commands/e2e for workspace use; omitted from publishConfig.exports.
• Thin product smoke tests: packages/cli (bl) and packages/rag (rag) each keep smoke e2e only—version, root help, command-surface wiring. Bl root help asserts one representative command per group in groups.ts.
• Config & docs: Root pnpm test runs commands + cli + rag e2e; all packages share the same globalSetup. Updated AGENTS.md and docs/agents/cli-e2e-tests.md.
• Cleanup: Remove migrated e2e and obsolete cli unit tests (already covered by bailian-cli-runtime). Stress tests stay in packages/cli/tests/stress/ unchanged.

Notes

• Contract e2e validates command library behavior; smoke validates product wiring (which commands each binary exposes).
• Rag smoke asserts knowledge/auth are present and text/image/memory are absent.
• Live-integration failures (Console, video API, etc.) are environment-dependent, same as before migration.