add link picker and validation to navigation editor

- replace freeform inputs with grouped dropdown (pages, custom pages,
  collections, external URL)
- add inline URL validation for external links
- add inline feedback component instead of flash messages
- add dismiss-on-interaction pattern (feedback clears on changes)
- add no-JS fallback via NavigationController
- add DirtyGuard hook to warn before navigating away with unsaved changes
- add no-JS fallbacks for settings forms (from address, signing secret)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

test/berrypod_web/live/admin/navigation_test.exs

@@ -58,9 +58,9 @@ defmodule BerrypodWeb.Admin.NavigationTest do
 
       # Should have 5 items now (4 defaults + 1 new)
       html = render(view)
-      # New empty item has empty placeholder inputs
-      assert Regex.scan(~r/phx-value-section="header".*?phx-value-field="label"/, html)
-             |> length() == 5
+      # Count header item forms by their phx-value-section attribute
+      assert Regex.scan(~r/phx-value-section="header".*?phx-value-index/, html)
+             |> length() >= 5
     end
 
     test "removing an item removes from list", %{conn: conn} do
@@ -92,15 +92,13 @@ defmodule BerrypodWeb.Admin.NavigationTest do
       assert Enum.at(items, 1)["label"] == "Home"
     end
 
-    test "adding a custom page creates nav item", %{conn: conn} do
+    test "custom pages appear in destination dropdown", %{conn: conn} do
       {:ok, _} = Pages.create_custom_page(%{slug: "faq", title: "FAQ"})
 
-      {:ok, view, _html} = live(conn, ~p"/admin/navigation")
+      {:ok, _view, html} = live(conn, ~p"/admin/navigation")
 
-      render_click(view, "add_page", %{"section" => "header", "slug" => "faq"})
-
-      html = render(view)
-      assert html =~ ~s(value="FAQ")
+      # Custom page should appear in the dropdown options
+      assert html =~ "FAQ"
       assert html =~ ~s(value="/faq")
     end
 
@@ -110,7 +108,8 @@ defmodule BerrypodWeb.Admin.NavigationTest do
       render_click(view, "remove_item", %{"section" => "footer", "index" => "0"})
       render_click(view, "save")
 
-      assert render(view) =~ "Navigation saved"
+      # Inline feedback shows "Saved"
+      assert has_element?(view, ".admin-inline-feedback-saved", "Saved")
 
       items = Settings.get_setting("footer_nav")
       assert length(items) == 3
@@ -150,6 +149,14 @@ defmodule BerrypodWeb.Admin.NavigationTest do
       render_click(view, "add_item", %{"section" => "header"})
       assert has_element?(view, ".admin-badge-warning")
 
+      # Fill in required fields for the new item before saving
+      render_change(view, "nav_item_change", %{
+        "section" => "header",
+        "index" => "4",
+        "label" => "Test",
+        "dest" => "/"
+      })
+
       render_click(view, "save")
       refute has_element?(view, ".admin-badge-warning")
     end