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/web/tracker/presenters/src/lib/pages/issue.page.scss

@@ -338,3 +338,10 @@ a.ts-key {
   font-size: 0.8125rem;
   color: var(--ts-brand);
 }
+
+.ts-attachments {
+  display: grid;
+  grid-template-columns: repeat(auto-fill, minmax(16rem, 1fr));
+  gap: 0.5rem;
+  margin: 0.5rem 0;
+}