refactor: move inline tests to separate files via #[path]

crates/tui/src/config.rs

@@ -78,21 +78,5 @@ impl Config {
 }
 
 #[cfg(test)]
-mod tests {
-    use super::*;
-
-    #[test]
-    fn config_roundtrip() {
-        let config = Config {
-            api_url: "http://localhost:3000".into(),
-        };
-        let json = serde_json::to_string(&config).unwrap();
-        let decoded: Config = serde_json::from_str(&json).unwrap();
-        assert_eq!(decoded.api_url, "http://localhost:3000");
-    }
-
-    #[test]
-    fn load_returns_none_when_no_file() {
-        let _ = Config::load();
-    }
-}
+#[path = "tests/config.rs"]
+mod tests;