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/presenters/src/lib/graphql/issue.resolver.ts

@@ -183,6 +183,18 @@ export class IssueResolver {
     );
   }
 
+  @Mutation(() => CommandResultGql, {
+    description:
+      'Remove a file from a ticket (whoever uploaded it, or an owner/admin). Upload with the REST API.',
+  })
+  removeAttachment(
+    @CurrentUser() me: User,
+    @Args('issueId', { type: () => ID }) issueId: string,
+    @Args('attachmentId', { type: () => ID }) attachmentId: string,
+  ) {
+    return this.issuesService.detach(me.id, issueId, attachmentId);
+  }
+
   @Mutation(() => CommandResultGql, {
     description: 'Assign (or unassign with null) a project member',
   })