add admin email settings page with provider selection

Card radio component for picking email providers (SMTP, SendGrid, Mailjet, etc.)
with instant client-side switching via JS hook. Adapter configs are pre-rendered
and toggled without a server round-trip. Secrets are preserved when re-saving
with blank password fields. Includes from address field, test email sending,
and disconnect flow.

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

lib/berrypod_web/components/core_components.ex

@@ -519,6 +519,99 @@ defmodule BerrypodWeb.CoreComponents do
     """
   end
 
+  @doc """
+  Renders a radio card group — a set of selectable cards backed by radio inputs.
+
+  Each option is a map with `:value` and `:name`, plus optional `:description`,
+  `:tags`, `:url`, `:badge`, and `:disabled` keys.
+
+  The `display` attr controls card content layout:
+  - `:tags` (default) — name + tag pills + short description
+  - `:description` — name + description text + link
+
+  ## Examples
+
+      <.card_radio_group
+        name="email[adapter]"
+        value={@selected}
+        legend="Email provider"
+        options={[
+          %{value: "postmark", name: "Postmark", description: "Fast email.", tags: ["Transactional", "US"]},
+          %{value: "smtp", name: "SMTP", description: "Any SMTP server.", tags: ["Any type"]}
+        ]}
+      />
+  """
+  attr :name, :string, required: true
+  attr :value, :string, default: nil
+  attr :legend, :string, required: true
+  attr :options, :list, required: true
+  attr :disabled, :boolean, default: false
+  attr :display, :atom, default: :tags, values: [:description, :tags]
+
+  def card_radio_group(assigns) do
+    ~H"""
+    <fieldset class="card-radio-fieldset" disabled={@disabled}>
+      <legend class="admin-label">{@legend}</legend>
+      <div class="card-radio-grid">
+        <label
+          :for={option <- @options}
+          class={[
+            "card-radio-card",
+            @value == option.value && "card-radio-card-selected",
+            option[:disabled] && "card-radio-card-disabled"
+          ]}
+        >
+          <input
+            type="radio"
+            id={"#{@name}-#{option.value}"}
+            name={@name}
+            value={option.value}
+            checked={@value == option.value}
+            disabled={option[:disabled] || @disabled}
+            class="card-radio-input"
+          />
+          <span class="card-radio-name">{option.name}</span>
+          <.card_radio_content option={option} display={@display} />
+        </label>
+      </div>
+    </fieldset>
+    """
+  end
+
+  attr :option, :map, required: true
+  attr :display, :atom, required: true
+
+  defp card_radio_content(%{display: :tags} = assigns) do
+    ~H"""
+    <span :if={@option[:tags]} class="card-radio-tags">
+      <span :for={tag <- @option.tags} class="card-radio-tag">{tag}</span>
+    </span>
+    <span :if={@option[:description]} class="card-radio-description">
+      {@option.description}
+    </span>
+    <span :if={@option[:badge]} class="card-radio-badge">{@option.badge}</span>
+    """
+  end
+
+  defp card_radio_content(assigns) do
+    ~H"""
+    <span :if={@option[:description]} class="card-radio-description">
+      {@option.description}
+    </span>
+    <span :if={@option[:badge]} class="card-radio-badge">{@option.badge}</span>
+    <a
+      :if={@option[:url]}
+      href={@option.url}
+      target="_blank"
+      rel="noopener"
+      class="card-radio-link"
+      onclick="event.stopPropagation();"
+    >
+      {@option.name} &nearr;
+    </a>
+    """
+  end
+
   def show_modal(js \\ %JS{}, id) when is_binary(id) do
     js
     |> JS.exec("showModal()", to: "##{id}")