Add phx.gen.auth authentication scaffolding

- LiveView-based email/password auth via mix phx.gen.auth
- Auth links removed from public navigation (direct URL access only)
- Accounts context with User schema and token management

app/lib/firehose_web/controllers/user_settings_controller.ex

@@ -0,0 +1,77 @@
+defmodule FirehoseWeb.UserSettingsController do
+  use FirehoseWeb, :controller
+
+  alias Firehose.Accounts
+  alias FirehoseWeb.UserAuth
+
+  import FirehoseWeb.UserAuth, only: [require_sudo_mode: 2]
+
+  plug :require_sudo_mode
+  plug :assign_email_and_password_changesets
+
+  def edit(conn, _params) do
+    render(conn, :edit)
+  end
+
+  def update(conn, %{"action" => "update_email"} = params) do
+    %{"user" => user_params} = params
+    user = conn.assigns.current_scope.user
+
+    case Accounts.change_user_email(user, user_params) do
+      %{valid?: true} = changeset ->
+        Accounts.deliver_user_update_email_instructions(
+          Ecto.Changeset.apply_action!(changeset, :insert),
+          user.email,
+          &url(~p"/users/settings/confirm-email/#{&1}")
+        )
+
+        conn
+        |> put_flash(
+          :info,
+          "A link to confirm your email change has been sent to the new address."
+        )
+        |> redirect(to: ~p"/users/settings")
+
+      changeset ->
+        render(conn, :edit, email_changeset: %{changeset | action: :insert})
+    end
+  end
+
+  def update(conn, %{"action" => "update_password"} = params) do
+    %{"user" => user_params} = params
+    user = conn.assigns.current_scope.user
+
+    case Accounts.update_user_password(user, user_params) do
+      {:ok, {user, _}} ->
+        conn
+        |> put_flash(:info, "Password updated successfully.")
+        |> put_session(:user_return_to, ~p"/users/settings")
+        |> UserAuth.log_in_user(user)
+
+      {:error, changeset} ->
+        render(conn, :edit, password_changeset: changeset)
+    end
+  end
+
+  def confirm_email(conn, %{"token" => token}) do
+    case Accounts.update_user_email(conn.assigns.current_scope.user, token) do
+      {:ok, _user} ->
+        conn
+        |> put_flash(:info, "Email changed successfully.")
+        |> redirect(to: ~p"/users/settings")
+
+      {:error, _} ->
+        conn
+        |> put_flash(:error, "Email change link is invalid or it has expired.")
+        |> redirect(to: ~p"/users/settings")
+    end
+  end
+
+  defp assign_email_and_password_changesets(conn, _opts) do
+    user = conn.assigns.current_scope.user
+
+    conn
+    |> assign(:email_changeset, Accounts.change_user_email(user))
+    |> assign(:password_changeset, Accounts.change_user_password(user))
+  end
+end