- ZULIP_API_KEY: no longer SystemExit, now reports 'credential-missing: ZULIP_API_KEY'
- EMAIL_PASSWORD: no longer sys.exit(1), now appends to DEGRADED_LEGS and returns success
- PVE API: fixed None check in storage section
- Summary: reports degraded legs before summary
This allows the digest to be produced and emailed even when credentials are missing,
while still explicitly logging which legs are degraded.
Test: empty env produces JSON report + degraded leg labels, no SystemExit.
root