CheckUsernameAsync returned false (taken) on any API failure, making every
username appear taken when SilverDESK was unreachable. Now returns nullable
bool so errors show a warning instead of blocking submission.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Add developer application page with form submission that creates tickets
in SilverDESK. Includes provisioning service scaffolding for Mattermost,
Mailcow, and Gitea account creation. Fixes API key header casing
(X-API-Key) and ticket payload to match SilverDESK's CreateTicketDto
contract.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>