Add cargo fmt hook for Claude Code, fix formatting

Configure .claude/settings.json to run cargo fmt after editing .rs files.
Apply formatting fix to long line in integration tests.

Author: gordonwoodhull

.claude/settings.json

@@ -0,0 +1,10 @@
+{
+  "hooks": {
+    "afterEdit": [
+      {
+        "matcher": "*.rs",
+        "command": "cargo fmt"
+      }
+    ]
+  }
+}

tests/integration.rs

@@ -342,7 +342,10 @@ my-pkg = "{}"
     fn empty_config_does_nothing() {
         let cache_dir = TempDir::new().unwrap();
 
-        let toml = format!(r#"destination = "{}""#, cache_dir.path().display().to_string().replace('\\', "/"));
+        let toml = format!(
+            r#"destination = "{}""#,
+            cache_dir.path().display().to_string().replace('\\', "/")
+        );
         let config = Config::parse(&toml).unwrap();
         let dest = config.destination.clone().unwrap();
         let configured_local: HashSet<String> = config.local.keys().cloned().collect();