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>

lang/ca/rules.php

@@ -48,6 +48,14 @@ return [
         'event' => '«:event» no és un esdeveniment al qual subscriure\'s.',
     ],
 
+    'taskstream' => [
+        'machine' => 'TaskStream només entén tokens de Pireon: entra amb un, o configura TASKSTREAM_TOKEN per als tokens de màquina.',
+        'key_needed' => 'No es pot treure una clau de l\'slug: indica\'n una a «taskstream_key» (de 2 a 10 lletres o xifres, començant per lletra).',
+        'refused' => 'TaskStream no ha creat el projecte: :reason',
+        'unauthorised' => 'TaskStream ha rebutjat el token: potser ha caducat o no hi té accés.',
+        'unavailable' => 'TaskStream no respon ara mateix; no s\'ha creat res, torna-ho a provar d\'aquí a una estona.',
+    ],
+
     'tokens' => [
         'ability' => '«:ability» no és un permís que tinguis, així que un token teu no el pot tenir.',
         'machine' => 'Els tokens els gestiona una persona, no un altre token.',