feat(contacts): per-month bar chart on the /contacts page

Aggregates contact counts by calendar month summed across every
year, rendered as an inline SVG bar chart above the table. Months
with no contacts render as a 0-height tick so the x-axis stays
continuous at 12 bars.

Respects the same scope visibility the table uses, so private
contacts a viewer can't see don't leak into the chart counts.
Each <rect> carries data-month / data-month-count for testability
and a <title> for hover.

lib/microwaveprop_web/live/contact_live/index.ex

@@ -50,6 +50,16 @@ defmodule MicrowavepropWeb.ContactLive.Index do
     ]
   end
 
+  # Monthly chart geometry. Module attributes so the SVG layout
+  # constants stay in one place; assigns wire the values that the
+  # template renders into the markup.
+  @month_labels ~w(Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec)
+  @chart_max_bar_height 150
+  @chart_bar_width 36
+  @chart_bar_pitch 50
+  @chart_bar_offset 12
+  @chart_baseline 180
+
   @impl true
   def mount(_params, _session, socket) do
     scope = socket.assigns[:current_scope]
@@ -60,10 +70,44 @@ defmodule MicrowavepropWeb.ContactLive.Index do
      socket
      |> assign(:page_title, "Contacts")
      |> assign(:total_contacts, total)
+     |> assign(:monthly_bars, monthly_bars(scope))
+     |> assign(:chart_baseline, @chart_baseline)
+     |> assign(:chart_bar_width, @chart_bar_width)
      |> assign(:visible_fields, visible_fields_for(scope))
      |> assign(:data_provider, {__MODULE__, :visible_query_provider, [scope_token(scope)]})}
   end
 
+  defp monthly_bars(scope) do
+    by_month =
+      scope
+      |> visible_query()
+      |> where([c], not is_nil(c.qso_timestamp))
+      |> group_by([c], fragment("EXTRACT(MONTH FROM ?)::int", c.qso_timestamp))
+      |> select([c], {fragment("EXTRACT(MONTH FROM ?)::int", c.qso_timestamp), count(c.id)})
+      |> Repo.all()
+      |> Map.new()
+
+    counts = Enum.map(1..12, fn m -> {m, Map.get(by_month, m, 0)} end)
+    max_count = counts |> Enum.map(&elem(&1, 1)) |> Enum.max()
+
+    Enum.map(counts, fn {month, count} ->
+      x = (month - 1) * @chart_bar_pitch + @chart_bar_offset
+      height = bar_height(count, max_count)
+
+      %{
+        month: month,
+        label: Enum.at(@month_labels, month - 1),
+        count: count,
+        x: x,
+        y: @chart_baseline - height,
+        height: height
+      }
+    end)
+  end
+
+  defp bar_height(_count, 0), do: 0
+  defp bar_height(count, max_count), do: round(count / max_count * @chart_max_bar_height)
+
   # Hide the Private column entirely unless this scope can actually see
   # at least one private contact — avoids an always-empty column for
   # visitors and owners who've never flagged one as private.
@@ -193,6 +237,53 @@ defmodule MicrowavepropWeb.ContactLive.Index do
         </:actions>
       </.header>
 
+      <section class="bg-base-200 rounded-lg p-4 mb-6">
+        <h3 class="text-sm font-semibold opacity-70 uppercase tracking-wide mb-3">
+          Contacts by month <span class="text-xs font-normal opacity-60">(all years combined)</span>
+        </h3>
+        <svg viewBox="0 0 612 220" class="w-full h-48" role="img" aria-label="Monthly contact counts">
+          <line
+            x1="0"
+            y1={@chart_baseline}
+            x2="612"
+            y2={@chart_baseline}
+            class="stroke-base-content/30"
+            stroke-width="1"
+          />
+          <%= for bar <- @monthly_bars do %>
+            <rect
+              x={bar.x}
+              y={bar.y}
+              width={@chart_bar_width}
+              height={bar.height}
+              class="fill-primary"
+              data-month={bar.month}
+              data-month-count={bar.count}
+            >
+              <title>{bar.label}: {bar.count}</title>
+            </rect>
+            <text
+              x={bar.x + @chart_bar_width / 2}
+              y={@chart_baseline + 16}
+              text-anchor="middle"
+              class="fill-base-content text-xs"
+            >
+              {bar.label}
+            </text>
+            <%= if bar.count > 0 do %>
+              <text
+                x={bar.x + @chart_bar_width / 2}
+                y={bar.y - 4}
+                text-anchor="middle"
+                class="fill-base-content text-xs"
+              >
+                {bar.count}
+              </text>
+            <% end %>
+          <% end %>
+        </svg>
+      </section>
+
       <.live_table
         fields={@visible_fields}
         filters={filters()}

test/microwaveprop_web/live/contact_live_test.exs

@@ -116,6 +116,26 @@ defmodule MicrowavepropWeb.ContactLiveTest do
       {:ok, _lv, html2} = live(conn, ~p"/contacts?page=2")
       assert html2 =~ "Page"
     end
+
+    test "renders a per-month bar chart that sums across years", %{conn: conn} do
+      # Two March contacts in different years (2025, 2026) plus one
+      # July: chart should report Mar=2 and Jul=1.
+      create_contact(%{qso_timestamp: ~U[2025-03-15 12:00:00Z], station1: "W5MAR"})
+      create_contact(%{qso_timestamp: ~U[2026-03-22 12:00:00Z], station1: "K5MAR"})
+      create_contact(%{qso_timestamp: ~U[2026-07-10 12:00:00Z], station1: "W5JUL"})
+
+      {:ok, _lv, html} = live(conn, ~p"/contacts")
+
+      assert html =~ "Contacts by month"
+      assert html =~ ~s|data-month="3"|
+      assert html =~ ~s|data-month-count="2"|
+      assert html =~ ~s|data-month="7"|
+      assert html =~ ~s|data-month-count="1"|
+      # Months without contacts still render with a 0 count so the
+      # x-axis stays continuous.
+      assert html =~ ~s|data-month="1"|
+      assert html =~ ~s|data-month-count="0"|
+    end
   end
 
   describe "Index private visibility" do