Stop tracking built binary in build/

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.gitignore

@@ -1,23 +1,2 @@
-# ---> Rust
-# Generated by Cargo
-# will have compiled files and executables
-debug/
-target/
-
-# These are backup files generated by rustfmt
-**/*.rs.bk
-
-# MSVC Windows builds of rustc generate these, which store debugging information
-*.pdb
-
-# RustRover
-#  JetBrains specific template is maintained in a separate JetBrains.gitignore that can
-#  be found at https://github.com/github/gitignore/blob/main/Global/JetBrains.gitignore
-#  and can be added to the global gitignore or merged into this file.  For a more nuclear
-#  option (not recommended) you can uncomment the following to ignore the entire idea folder.
-#.idea/
-
-
-# Added by cargo
-
 /target
+/build