Initial commit

CalDAV and CardDAV checkers sharing a single Go module. Discovery follows
RFC 6764 (/.well-known + SRV/TXT), authenticated probes cover principal,
home-set, collections and a minimal REPORT query on top of go-webdav.
Common shape in internal/dav/; CalDAV adds a scheduling rule.

Surfaces its context URL (and each secure-SRV target) as TLS endpoints via
the EndpointDiscoverer interface, so the dedicated TLS checker can pick
them up without re-parsing observations.

HTML report foregrounds common misconfigs (well-known returning 200,
missing SRV, plaintext-only SRV, missing DAV capability, skipped auth
phase) as action-item callouts before the full phase breakdown.

caldav/types.go

@@ -0,0 +1,9 @@
+// Package caldav wires the CalDAV-specific options, collect pipeline,
+// rules, and HTML report on top of the shared helpers in internal/dav.
+package caldav
+
+import "git.happydns.org/checker-dav/internal/dav"
+
+const ObservationKey = "caldav"
+
+type Data = dav.Observation