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_sources.go

@@ -0,0 +1,34 @@
+package http
+
+import (
+	"log/slog"
+	stdhttp "net/http"
+)
+
+// ui_sources.go — HTML form-driven source-group CRUD. Slice 1 of
+// P2R-02 lights the tab; slice 2 fills in list, new, edit, delete,
+// and per-group Run-now.
+
+type hostSourcesPage struct {
+	hostChromeData
+}
+
+func (s *Server) handleUIHostSources(w stdhttp.ResponseWriter, r *stdhttp.Request) {
+	u := s.requireUIUser(w, r)
+	if u == nil {
+		return
+	}
+	host, ok := s.loadHostForUI(w, r)
+	if !ok {
+		return
+	}
+	view := s.baseView(u, "dashboard")
+	view.Title = host.Name + " sources · restic-manager"
+	view.Page = hostSourcesPage{
+		hostChromeData: s.loadHostChrome(r, *host, "sources", "sources"),
+	}
+	if err := s.deps.UI.Render(w, "host_sources", view); err != nil {
+		slog.Error("ui: render host_sources", "err", err)
+		stdhttp.Error(w, "internal", stdhttp.StatusInternalServerError)
+	}
+}