Open a TaskStream board from the panel's project form

A "TaskStream" section on the create form (toggle and optional key,
suggested from the slug) opens the board before saving, as the person
signed in, with the Pireon token of their session. A refusal shows on the
key field and a TaskStream outage as a notification; either way nothing is
saved. The created notification carries the link, and the edit page has
an "Open in TaskStream" button.

Documented in the user manual (and its PDF) and the README.

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

lang/en/panel.php

@@ -519,6 +519,15 @@ return [
             'needs_help' => 'Looking for help',
             'needs_help_hint' => 'Surfaces it in the contribute section of the site.',
         ],
+        'taskstream' => [
+            'section' => 'TaskStream',
+            'section_hint' => 'A public board in TaskStream, the collective\'s issue tracker, in your name.',
+            'toggle' => 'Also create it in TaskStream',
+            'key' => 'Key in TaskStream',
+            'key_hint' => '2 to 10 letters or digits, starting with a letter. Left empty, it is made from the slug.',
+            'created' => 'Board created in TaskStream: :url',
+            'open' => 'Open in TaskStream',
+        ],
         'filters' => ['unpublished' => 'Unpublished'],
         'actions' => ['publish' => 'Publish'],
     ],