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>

lib/berrypod_web/controllers/navigation_controller.ex

@@ -0,0 +1,81 @@
+defmodule BerrypodWeb.NavigationController do
+  @moduledoc """
+  No-JS fallback for navigation form submission.
+
+  With JS enabled, the LiveView handles everything. Without JS,
+  the form POSTs here and we redirect back to the LiveView page.
+  """
+  use BerrypodWeb, :controller
+
+  alias Berrypod.Settings
+
+  def save(conn, %{"header_nav" => header_json, "footer_nav" => footer_json}) do
+    with {:ok, header_items} <- Jason.decode(header_json),
+         {:ok, footer_items} <- Jason.decode(footer_json) do
+      all_items = header_items ++ footer_items
+      errors = validate_nav_items(all_items)
+
+      if errors == [] do
+        Settings.put_setting("header_nav", header_items, "json")
+        Settings.put_setting("footer_nav", footer_items, "json")
+
+        conn
+        |> put_flash(:info, "Navigation saved")
+        |> redirect(to: ~p"/admin/navigation")
+      else
+        conn
+        |> put_flash(:error, Enum.join(errors, ". "))
+        |> redirect(to: ~p"/admin/navigation")
+      end
+    else
+      {:error, _} ->
+        conn
+        |> put_flash(:error, "Invalid navigation data")
+        |> redirect(to: ~p"/admin/navigation")
+    end
+  end
+
+  defp validate_nav_items(items) do
+    items
+    |> Enum.flat_map(fn item ->
+      cond do
+        item["label"] == "" || item["label"] == nil ->
+          ["All links need a label"]
+
+        item["href"] == "" || item["href"] == nil ->
+          ["\"#{item["label"]}\" needs a destination"]
+
+        item["external"] == true || is_external_url?(item["href"]) ->
+          if valid_url?(item["href"]) do
+            []
+          else
+            ["\"#{item["label"]}\" has an invalid URL"]
+          end
+
+        true ->
+          []
+      end
+    end)
+    |> Enum.uniq()
+  end
+
+  defp valid_url?(url) when is_binary(url) do
+    case URI.parse(url) do
+      %URI{scheme: scheme, host: host}
+      when scheme in ["http", "https"] and is_binary(host) and host != "" ->
+        true
+
+      _ ->
+        false
+    end
+  end
+
+  defp valid_url?(_), do: false
+
+  defp is_external_url?(nil), do: false
+  defp is_external_url?(""), do: false
+
+  defp is_external_url?(href) do
+    String.starts_with?(href, "http://") || String.starts_with?(href, "https://")
+  end
+end

lib/berrypod_web/controllers/settings_controller.ex

@@ -0,0 +1,42 @@
+defmodule BerrypodWeb.SettingsController do
+  @moduledoc """
+  No-JS fallback for settings form submissions.
+
+  With JS enabled, the LiveView handles everything. Without JS,
+  the forms POST here and we redirect back to the LiveView page.
+  """
+  use BerrypodWeb, :controller
+
+  alias Berrypod.Settings
+  alias Berrypod.Stripe.Setup, as: StripeSetup
+
+  def update_from_address(conn, %{"from_address" => address}) do
+    address = String.trim(address)
+
+    if address != "" do
+      Settings.put_setting("email_from_address", address)
+
+      conn
+      |> put_flash(:info, "From address saved")
+      |> redirect(to: ~p"/admin/settings")
+    else
+      conn
+      |> put_flash(:error, "From address can't be blank")
+      |> redirect(to: ~p"/admin/settings")
+    end
+  end
+
+  def update_signing_secret(conn, %{"webhook" => %{"signing_secret" => secret}}) do
+    if secret == "" do
+      conn
+      |> put_flash(:error, "Please enter a signing secret")
+      |> redirect(to: ~p"/admin/settings")
+    else
+      StripeSetup.save_signing_secret(secret)
+
+      conn
+      |> put_flash(:info, "Signing secret saved")
+      |> redirect(to: ~p"/admin/settings")
+    end
+  end
+end