feat(map): show last-deployed stamp in map sidebar

Deploy stamp was in Layouts.app's nav but the map page uses a custom
full-screen layout that skips the standard nav, so the info wasn't
visible on the page most users land on. Add a compact
"Deployed 2h ago" under the sidebar's data-timestamp/pipeline-status
block with the full UTC time as a tooltip, matching the shape of
Layouts.deploy_stamp.

lib/microwaveprop_web/live/map_live.ex

@@ -71,6 +71,8 @@ defmodule MicrowavepropWeb.MapLive do
     # wrong viewport and forecast-hour clicks show a small square of
     # coverage instead of the full map.
 
+    build_ts = Microwaveprop.Application.build_timestamp()
+
     {:ok,
      assign(socket,
        page_title: "Propagation Prediction Map",
@@ -85,10 +87,26 @@ defmodule MicrowavepropWeb.MapLive do
        outside_conus: outside_conus?(visitor),
        grid_visible: false,
        radar_visible: false,
-       antenna_height_ft: 33
+       antenna_height_ft: 33,
+       deploy_iso: Calendar.strftime(build_ts, "%Y-%m-%d %H:%M UTC"),
+       deploy_ago: format_deploy_ago(build_ts)
      )}
   end
 
+  # Compact relative-time rendering of the build timestamp. Matches the
+  # format used by Layouts.deploy_stamp/1 so the nav and the map
+  # sidebar stay consistent.
+  defp format_deploy_ago(%DateTime{} = dt) do
+    diff = max(DateTime.diff(DateTime.utc_now(), dt, :second), 0)
+
+    cond do
+      diff < 60 -> "just now"
+      diff < 3600 -> "#{div(diff, 60)}m ago"
+      diff < 86_400 -> "#{div(diff, 3600)}h ago"
+      true -> "#{div(diff, 86_400)}d ago"
+    end
+  end
+
   # Prefer the visitor's Cloudflare geolocation when present; fall back to DFW.
   defp initial_center(%{"cf_lat" => lat, "cf_lon" => lon}) when is_float(lat) and is_float(lon) do
     %{lat: lat, lon: lon}
@@ -879,6 +897,13 @@ defmodule MicrowavepropWeb.MapLive do
               status={@pipeline_status}
               progress={@pipeline_progress}
             />
+
+            <div
+              class="text-[11px] opacity-60 px-1 pt-2 leading-tight"
+              title={"Last deployed #{@deploy_iso}"}
+            >
+              Deployed {@deploy_ago}
+            </div>
           </div>
         </div>
       </div>