chore(boxed): track Windows agent installers again

Empty .gitignore and commit edon-agent-setup-0.1.0.exe plus the
edon-agent-win64.exe symlink, reversing the previous decision to keep
the Windows installers out of git history.

.gitignore

@@ -1,5 +0,0 @@
-# Windows agent installers are published to boxed/ by the edon-agent-windows
-# build and served from disk; keep the (large, frequently rebuilt) binaries out
-# of git history. Other boxed/ artifacts (.deb, .rpm, restic, checksums) stay tracked.
-/boxed/edon-agent-setup-*.exe
-/boxed/edon-agent-win64.exe

boxed/edon-agent-win64.exe

@@ -0,0 +1 @@
+edon-agent-setup-0.1.0.exe