When user runs
✓ Memory provider: built-in only
Saved to config.yaml and leaves the API key blank,
the old code skipped writing it entirely. This caused the uvx daemon
launcher to fail at startup because it couldn't distinguish between
"key not configured" and "explicitly blank key."
Now HINDSIGHT_LLM_API_KEY is always written to .env so the value
is either set or explicitly empty.