Open a TaskStream board when a project is created through the API

`taskstream: true` on POST /v1/projects also creates the project in
TaskStream, public, as the caller (their Pireon token is passed on), and
the answer carries `taskstream_key` and `taskstream_url`. The key is
`taskstream_key` or one made from the default-language slug.

The board is opened before the project is saved: if TaskStream refuses
it, nothing is created here and the reason comes back as a validation
error (502 when TaskStream does not answer). Machine tokens need the
server's own TASKSTREAM_TOKEN. Updates ignore the flag, and duplicates do
not inherit the link.

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

app/Services/TaskStream/TaskStreamException.php

@@ -0,0 +1,41 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Services\TaskStream;
+
+use RuntimeException;
+use Throwable;
+
+class TaskStreamException extends RuntimeException
+{
+    public function __construct(
+        string $message,
+        public readonly ?int $status = null,
+        ?Throwable $previous = null,
+    ) {
+        parent::__construct($message, $status ?? 0, $previous);
+    }
+
+    /**
+     * TaskStream refused what it was asked for (a key in use, a bad name):
+     * the caller can fix it and try again.
+     */
+    public function isRefusal(): bool
+    {
+        return in_array($this->status, [400, 409, 422], true);
+    }
+
+    /**
+     * The token was not good enough there: expired, or without access.
+     */
+    public function isUnauthorised(): bool
+    {
+        return in_array($this->status, [401, 403], true);
+    }
+
+    public static function unreachable(string $url, ?Throwable $previous = null): self
+    {
+        return new self("TaskStream could not be reached at [{$url}].", previous: $previous);
+    }
+}