Offer «Entrar con Pireon» on the panel's login page

Under the e-mail and password form, a button takes the redirect flow
(Authorization Code + PKCE), so the password is only ever typed at the
identity server. The routes for it were already there; the page had no
way to reach them.

A Pireon client allows one grant type and the panel's is a password
client, so the redirect flow can use its own: PIREON_REDIRECT_CLIENT_ID
and PIREON_REDIRECT_CLIENT_SECRET (the main client when they are empty).
The button shows up once that client is set, or with
PIREON_REDIRECT_LOGIN=true. Each session renews its token with the
client that issued it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

app/Services/Pireon/PireonClient.php

@@ -37,6 +37,22 @@ class PireonClient
         );
     }
 
+    /**
+     * The client for the redirect flow: its own when PIREON_REDIRECT_CLIENT_ID
+     * is set (a Pireon client allows one grant type), the main one otherwise.
+     */
+    public static function forRedirect(): self
+    {
+        $own = filled(config('pireon.redirect_client_id'));
+
+        return new self(
+            server: (string) config('pireon.server'),
+            clientId: $own ? config('pireon.redirect_client_id') : config('pireon.client_id'),
+            clientSecret: $own ? config('pireon.redirect_client_secret') : config('pireon.client_secret'),
+            redirectUri: (string) config('pireon.redirect_uri'),
+        );
+    }
+
     public function isConfigured(): bool
     {
         return filled($this->clientId);