chore: untrack dist/ so CI stops shipping ~30MB of stale artifacts

dist/ was tracked, so every fresh CI checkout started with the old
Apr/Jun 2026 binaries + smpl-apps-0.7.0-x86_64.tar.gz already
present. The release job then:
  1. mkdir -p dist          (no-op — dir already exists with junk)
  2. cp fresh bins to dist/ (overwrites the stale binaries)
  3. tar -C dist .          (also picks up smpl-apps-0.7.0.tar.gz)
so every smpl-apps-VERSION-x86_64.tar.gz shipped to the fleet
contained the stowaway ~30MB legacy tarball. Verified in v0.8.20
tarball listing before this fix.

Untracks the whole directory and adds /dist/ to .gitignore so the
mistake can never come back. Next release will drop ~30MB per fleet
download and one confusing legacy artifact from every install.

Author: KonTy

.gitignore

@@ -1,3 +1,8 @@
 /target/
 **/target/
 */Cargo.lock
+
+# Release staging dir populated fresh by CI; must never contain
+# checked-in binaries or old tarballs (was accidentally shipping
+# ~30MB of stale artifacts inside every smpl-apps release tarball).
+/dist/