P2R-02 slice 1: host-detail sub-tab skeleton

Extract header/vitals/sub-tabs into a host_chrome partial that every
host-detail tab page renders. Sources / Schedules / Repo go from
inert divs to real <a> links backed by stub pages that share the
chrome and a 'coming next' body — slices 2/3/4 fill them in.

Also re-establishes the version indicator (host_schedule_version vs
agent's applied_schedule_version) in the header.

Drops the legacy fat-schedule list/edit templates that referenced
fields removed by the P2 redesign (Manual / Paths / RetentionPolicy
on Schedule); the new templates land in slice 3.

internal/server/http/ui_handlers.go

@@ -397,9 +397,44 @@ type awaitingFragment struct {
 	LastSeenAt *time.Time
 }
 
+// hostChromeData is the field set the host_chrome partial reads from
+// every host-detail-tab page's Page struct. Embed it as the first
+// (anonymous) field of the page struct so .Page.Host / .Page.SubTab
+// resolve via field promotion in the template.
+type hostChromeData struct {
+	Host             store.Host
+	SubTab           string // snapshots | sources | schedules | repo
+	Crumb            string // breadcrumb tail ("snapshots" / "sources" / etc)
+	SourceGroupCount int
+	ScheduleCount    int
+	ScheduleVersion  int64 // host_schedule_version (latest desired)
+}
+
+// loadHostChrome fetches the per-tab counts that every host-detail tab
+// renders in the chrome (sub-tab badges + version indicator). On any
+// non-fatal store error it logs and degrades to zeros — better to
+// render the page with stale counts than 500 the whole tab.
+func (s *Server) loadHostChrome(r *stdhttp.Request, host store.Host, subtab, crumb string) hostChromeData {
+	d := hostChromeData{Host: host, SubTab: subtab, Crumb: crumb}
+	if groups, err := s.deps.Store.ListSourceGroupsByHost(r.Context(), host.ID); err == nil {
+		d.SourceGroupCount = len(groups)
+	} else {
+		slog.Warn("ui chrome: list source groups", "host_id", host.ID, "err", err)
+	}
+	if scheds, err := s.deps.Store.ListSchedulesByHost(r.Context(), host.ID); err == nil {
+		d.ScheduleCount = len(scheds)
+	} else {
+		slog.Warn("ui chrome: list schedules", "host_id", host.ID, "err", err)
+	}
+	if v, err := s.deps.Store.GetHostScheduleVersion(r.Context(), host.ID); err == nil {
+		d.ScheduleVersion = v
+	}
+	return d
+}
+
 // hostDetailPage carries everything the host detail template needs.
 type hostDetailPage struct {
-	Host      store.Host
+	hostChromeData
 	Snapshots []store.Snapshot
 	// SnapshotsShown is the number rendered (we cap at ~50 for the
 	// first slice; pagination lands when it matters).
@@ -443,7 +478,7 @@ func (s *Server) handleUIHostDetail(w stdhttp.ResponseWriter, r *stdhttp.Request
 	view := s.baseView(u, "dashboard")
 	view.Title = host.Name + " · restic-manager"
 	view.Page = hostDetailPage{
-		Host:           *host,
+		hostChromeData: s.loadHostChrome(r, *host, "snapshots", "snapshots"),
 		Snapshots:      shown,
 		SnapshotsShown: len(shown),
 	}