App subscriptions: manage a user's subscriptions with the app's own token

- $user->appSubscriptions(): create (idempotency_key), find, all, checkout, revoke, pause,
  resume, update against /v1/client/subscriptions with a client credentials token, so apps don't
  depend on the user's login
- user id from the billable's anikeen_id (AnikeenId::useUserIdField())
- ApiException with status, stable error code, isNotFound/isConflict/isTemporary; network
  errors no longer escape as raw Guzzle exceptions
- rejected app tokens are renewed once; asApp() never changes the shared client's token
- tests (testbench + Guzzle mock) and CI

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

src/Id/Support/AppRequest.php

@@ -0,0 +1,62 @@
+<?php
+
+namespace Anikeen\Id\Support;
+
+use Anikeen\Id\AnikeenId;
+use Anikeen\Id\Contracts\AppTokenRepository;
+use Anikeen\Id\Exceptions\ApiException;
+use Anikeen\Id\Result;
+use GuzzleHttp\Exception\GuzzleException;
+use Throwable;
+
+/**
+ * Sends a request with the app's own token (client credentials). A rejected token is renewed
+ * once; every failure ends in an ApiException with status and error code.
+ */
+final class AppRequest
+{
+    /**
+     * @throws ApiException
+     */
+    public static function send(string $method, string $path, ?array $payload = null, array $query = []): Result
+    {
+        $result = self::attempt($method, $path, $payload, $query);
+
+        if ($result->status === 401) {
+            $tokens = app(AppTokenRepository::class);
+
+            if (method_exists($tokens, 'forgetAccessToken')) {
+                $tokens->forgetAccessToken();
+                $result = self::attempt($method, $path, $payload, $query);
+            }
+        }
+
+        if (!$result->success()) {
+            $body = is_object($result->data) ? $result->data : null;
+
+            throw new ApiException(
+                sprintf('Anikeen ID request %s %s failed: %s', $method, $path, $body->message ?? $result->error()),
+                $result->response()?->getStatusCode() ?? 0,
+                $body->error ?? null,
+                $result->exception,
+            );
+        }
+
+        return $result;
+    }
+
+    /**
+     * @throws ApiException
+     */
+    private static function attempt(string $method, string $path, ?array $payload, array $query): Result
+    {
+        try {
+            return app(AnikeenId::class)->asApp()->request($method, $path, $payload, $query);
+        } catch (ApiException $e) {
+            throw $e;
+        } catch (GuzzleException|Throwable $e) {
+            // network errors / timeouts (ConnectException isn't a RequestException) and token errors
+            throw new ApiException(sprintf('Anikeen ID is not reachable: %s', $e->getMessage()), 0, null, $e);
+        }
+    }
+}