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/event-handlers/activity-summary.ts

@@ -3,6 +3,8 @@ import {
   CommentDeletedEvent,
   CommentEditedEvent,
   IssueAssignedEvent,
+  IssueAttachmentAddedEvent,
+  IssueAttachmentRemovedEvent,
   IssueCreatedEvent,
   IssueLinkedEvent,
   IssueLinkType,
@@ -135,6 +137,11 @@ export function describeEvent(
       : `${actor} sacó ${issueKey} de su release`;
   }
 
+  if (event instanceof IssueAttachmentAddedEvent)
+    return `${actor} adjuntó ${event.attachment.fileName} a ${issueKey}`;
+  if (event instanceof IssueAttachmentRemovedEvent)
+    return `${actor} quitó el adjunto ${event.fileName} de ${issueKey}`;
+
   if (event instanceof CommentAddedEvent)
     return `${actor} comentó en ${issueKey}`;
   if (event instanceof CommentEditedEvent)