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.

carddav/discovery.go

@@ -0,0 +1,16 @@
+package carddav
+
+import (
+	"fmt"
+
+	"git.happydns.org/checker-dav/internal/dav"
+	sdk "git.happydns.org/checker-sdk-go/checker"
+)
+
+func (p *carddavProvider) DiscoverEntries(data any) ([]sdk.DiscoveryEntry, error) {
+	obs, ok := data.(*dav.Observation)
+	if !ok {
+		return nil, fmt.Errorf("unexpected data type %T", data)
+	}
+	return dav.DiscoverEntries(obs), nil
+}