POST /api/calendar/test issues a single PROPFIND with raw httpx
Basic auth. CalDAV servers configured for Digest (Baïkal default,
SabreDAV-based servers, Radicale with htdigest) reject Basic with
401, so the UI "Test connection" button surfaces "Auth failed —
check username/password" even when the URL and credentials are
correct.
src/caldav_sync.py (the real sync path) uses caldav.DAVClient,
which negotiates the scheme via niquests, so production sync
already works against these servers. The test endpoint just
doesn't match. Bring it to parity: keep the cheap Basic first
attempt, and on a 401-with-Digest-challenge retry once with
httpx.DigestAuth before deciding it's an auth failure.
Repro: configure CalDAV against a stock Baïkal install — test
button returns 401, sync succeeds.
Co-authored-by: Shatti2 <codered5678@gmail.com>
4ca3b38667