feat: attachments on tickets and comments

Files are uploaded over REST, stored on disk (a volume in Docker) and
recorded on the ticket as events; the bytes are written first, so no
attachment ever points at a missing file. Only images, video, audio, PDF
and plain text are shown inline, everything with nosniff and a sandbox CSP.
The web shows thumbnails, uploads by drag and drop or by pasting a
screenshot, and attaches files to new comments.

Also adds `nx run api:contracts`, which writes schema.gql and
openapi.json without starting the API or any database.

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

libs/api/tracker/application/src/lib/queries/query-handlers.ts

@@ -1,3 +1,4 @@
+import { GetAttachmentQueryHandler } from './get-attachment.query-handler';
 import { GetPublicProjectsQueryHandler } from './get-public-projects.query-handler';
 import { CanViewProjectQueryHandler } from './can-view-project.query-handler';
 import { GetActivityQueryHandler } from './get-activity.query-handler';
@@ -36,4 +37,5 @@ export const QUERY_HANDLERS = [
   GetUpcomingReleasesQueryHandler,
   SearchIssuesQueryHandler,
   SearchMyIssuesQueryHandler,
+  GetAttachmentQueryHandler,
 ];