chore: add compiled AniTrack binary to .gitignore

The project's compiled binary (AniTrack) was not covered by existing
gitignore patterns. Only platform-specific extensions like .exe, .dll,
.so, and .dylib were ignored. Add the bare binary name to prevent the
locally-built executable from appearing as an untracked file.

.gitignore

@@ -36,3 +36,4 @@ http-client.private.env.json
 
 # Build artifacts
 build/*.tar.gz
+AniTrack