tests: pin ink engine in _make_tui_argv npm-bootstrap tests (post-merge semantic fix)

Main's rewritten test_tui_npm_install.py tests call _make_tui_argv expecting
the Ink/npm flow unconditionally; with the dual-engine dispatch merged in,
_resolve_tui_engine() auto-selects opentui whenever ui-opentui/dist is built
in the repo, routing the call away from the path under test (first subprocess
became 'node --version' instead of 'npm run build'). Pin the engine to ink
via an autouse fixture, mirroring the existing pinning precedent in
test_tui_resume_flow.py.

plugins/memory/honcho/cli.py

@@ -416,6 +416,7 @@ def _ensure_sdk_installed() -> bool:
         [sys.executable, "-m", "pip", "install", "honcho-ai>=2.0.1"],
         capture_output=True,
         text=True,
+        stdin=subprocess.DEVNULL,
     )
     if result.returncode == 0:
         print("  Installed.\n")