checker: split monolithic rule into per-concern rules

Replace the single matrix_federation rule with individual rules for
federation status, well-known delegation, SRV records, connection
reachability, TLS checks, and homeserver version, so the UI surfaces a
clear checklist. Drop the incorrect well-known/server_name equality
check: m.server points at the delegated federation endpoint, which is
intentionally distinct from server_name.

checker/rules_version.go

@@ -0,0 +1,40 @@
+package checker
+
+import (
+	"context"
+	"fmt"
+	"strings"
+
+	sdk "git.happydns.org/checker-sdk-go/checker"
+)
+
+// versionRule reports whether the federation tester could fetch the
+// homeserver version string. The test probe reaches /_matrix/federation/v1/version,
+// so a failure here hints at a federation-path problem even when the rest
+// of the federation handshake looks healthy.
+type versionRule struct{}
+
+func (r *versionRule) Name() string { return "matrix.version" }
+func (r *versionRule) Description() string {
+	return "Checks that the homeserver responds to /_matrix/federation/v1/version and reports its name and version."
+}
+
+func (r *versionRule) Evaluate(ctx context.Context, obs sdk.ObservationGetter, _ sdk.CheckerOptions) []sdk.CheckState {
+	data, errSt := loadMatrixData(ctx, obs)
+	if errSt != nil {
+		return []sdk.CheckState{*errSt}
+	}
+
+	if data.Version.Error != "" {
+		return []sdk.CheckState{warnState("matrix.version.error", fmt.Sprintf("Homeserver /version probe failed: %s", data.Version.Error))}
+	}
+
+	version := strings.TrimSpace(data.Version.Name + " " + data.Version.Version)
+	if version == "" {
+		return []sdk.CheckState{infoState("matrix.version.unknown", "Homeserver did not return a version string.")}
+	}
+
+	st := passState("matrix.version.ok", fmt.Sprintf("Homeserver running %s.", version))
+	st.Meta = map[string]any{"version": version}
+	return []sdk.CheckState{st}
+}