Add root .gitignore to keep Rust target/ and common artifacts untracked

.gitignore

@@ -0,0 +1,19 @@
+# Rust build output
+target/
+**/target/
+
+# Cargo lock for libraries (optional; binary crates often commit Cargo.lock)
+# Cargo.lock
+
+# IDE / editor
+.idea/
+.vscode/
+*.swp
+*.swo
+*~
+.DS_Store
+
+# Environment and local overrides
+.env
+.env.local
+*.local