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>

database/migrations/2026_10_07_090000_link_projects_to_taskstream.php

@@ -0,0 +1,29 @@
+<?php
+
+declare(strict_types=1);
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+/**
+ * The board a project has in TaskStream, when it was opened from here: its
+ * id there, and the key its address is made from.
+ */
+return new class extends Migration
+{
+    public function up(): void
+    {
+        Schema::table('projects', function (Blueprint $table) {
+            $table->string('taskstream_project_id', 64)->nullable()->after('demo_url');
+            $table->string('taskstream_key', 10)->nullable()->after('taskstream_project_id');
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::table('projects', function (Blueprint $table) {
+            $table->dropColumn(['taskstream_project_id', 'taskstream_key']);
+        });
+    }
+};