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/report.go

@@ -0,0 +1,22 @@
+package caldav
+
+import (
+	"encoding/json"
+	"fmt"
+
+	sdk "git.happydns.org/checker-sdk-go/checker"
+
+	"git.happydns.org/checker-dav/internal/dav"
+)
+
+// GetHTMLReport delegates to the shared renderer so CalDAV and CardDAV
+// produce visually identical reports. Downstream TLS probes attached via
+// ctx.Related(dav.TLSRelatedKey) are folded in.
+func (p *caldavProvider) GetHTMLReport(ctx sdk.ReportContext) (string, error) {
+	var d dav.Observation
+	if err := json.Unmarshal(ctx.Data(), &d); err != nil {
+		return "", fmt.Errorf("failed to unmarshal caldav report: %w", err)
+	}
+	d.Kind = dav.KindCalDAV
+	return dav.RenderReport(&d, "CalDAV Server", ctx.Related(dav.TLSRelatedKey))
+}