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/commands/command-handlers.ts

@@ -25,6 +25,8 @@ import { PurgeCommentCommandHandler } from './purge-comment.command-handler';
 import { DropLinksToIssueCommandHandler } from './drop-links-to-issue.command-handler';
 import { DetachIssueFromReleaseCommandHandler } from './detach-issue-from-release.command-handler';
 import { UnassignIssueCommandHandler } from './unassign-issue.command-handler';
+import { AttachFileCommandHandler } from './attach-file.command-handler';
+import { DetachFileCommandHandler } from './detach-file.command-handler';
 
 export const COMMAND_HANDLERS = [
   CreateProjectCommandHandler,
@@ -55,4 +57,6 @@ export const COMMAND_HANDLERS = [
   DropLinksToIssueCommandHandler,
   DetachIssueFromReleaseCommandHandler,
   UnassignIssueCommandHandler,
+  AttachFileCommandHandler,
+  DetachFileCommandHandler,
 ];