Fix .gitignore: remove target files and add .jj exclusion

Author: hnlearndev

.gitignore

@@ -4,8 +4,8 @@
 
 # Rust build output
 /target/
+**/target/
 **/*.rs.bk
-
 # Cargo package files
 Cargo.lock
 
@@ -19,6 +19,9 @@ Cargo.lock
 *.swp
 *.swo
 
+# Jujutsu VCS files
+.jj/
+
 # Jupyter Notebook checkpoints
 .ipynb_checkpoints/