add entry/exit pages panel to analytics dashboard

ROW_NUMBER() window function picks first/last pageview per session.
Both tables live in the pages tab and support the pathname filter.
6 new tests, 1061 total.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/berrypod/analytics.ex

@@ -302,6 +302,68 @@ defmodule Berrypod.Analytics do
     |> Repo.one()
   end
 
+  @doc """
+  Top entry pages — the first page visited per session, by session count.
+  """
+  def entry_pages(date_range, opts \\ []) do
+    limit = Keyword.get(opts, :limit, 10)
+    filters = Keyword.get(opts, :filters, %{})
+
+    inner =
+      base_query(date_range, filters)
+      |> where([e], e.name == "pageview")
+      |> select([e], %{
+        session_hash: e.session_hash,
+        pathname: e.pathname,
+        rn:
+          fragment(
+            "ROW_NUMBER() OVER (PARTITION BY ? ORDER BY ? ASC)",
+            e.session_hash,
+            e.inserted_at
+          )
+      })
+
+    from(s in subquery(inner),
+      where: s.rn == 1,
+      group_by: s.pathname,
+      select: %{pathname: s.pathname, sessions: count()},
+      order_by: [desc: count()],
+      limit: ^limit
+    )
+    |> Repo.all()
+  end
+
+  @doc """
+  Top exit pages — the last page visited per session, by session count.
+  """
+  def exit_pages(date_range, opts \\ []) do
+    limit = Keyword.get(opts, :limit, 10)
+    filters = Keyword.get(opts, :filters, %{})
+
+    inner =
+      base_query(date_range, filters)
+      |> where([e], e.name == "pageview")
+      |> select([e], %{
+        session_hash: e.session_hash,
+        pathname: e.pathname,
+        rn:
+          fragment(
+            "ROW_NUMBER() OVER (PARTITION BY ? ORDER BY ? DESC)",
+            e.session_hash,
+            e.inserted_at
+          )
+      })
+
+    from(s in subquery(inner),
+      where: s.rn == 1,
+      group_by: s.pathname,
+      select: %{pathname: s.pathname, sessions: count()},
+      order_by: [desc: count()],
+      limit: ^limit
+    )
+    |> Repo.all()
+  end
+
   @doc """
   Deletes events older than the given datetime. Used by the retention worker.
   """