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/provider.go

@@ -0,0 +1,12 @@
+package carddav
+
+import (
+	sdk "git.happydns.org/checker-sdk-go/checker"
+)
+
+func Provider() sdk.ObservationProvider { return &carddavProvider{} }
+
+type carddavProvider struct{}
+
+func (p *carddavProvider) Key() sdk.ObservationKey            { return ObservationKey }
+func (p *carddavProvider) Definition() *sdk.CheckerDefinition { return Definition() }