feat(locations): remember last Add-window directory

Remember manually selected Add-window folders during the current session, with a persisted Locations toggle and cross-platform path handling.\n\nRefs #23

src-tauri/src/ipc.rs

@@ -291,6 +291,7 @@ pub struct PersistedSettings {
     pub proxy_port: u16,
     pub custom_user_agent: String,
     pub ask_where_to_save_each_file: bool,
+    pub remember_last_used_download_directory: bool,
     pub prevents_sleep_while_downloading: bool,
     pub media_cookie_source: MediaCookieSource,
     pub site_logins: Vec<SiteLogin>,

src-tauri/src/settings.rs

@@ -451,6 +451,7 @@ fn default_settings() -> PersistedSettings {
         proxy_port: 8080,
         custom_user_agent: String::new(),
         ask_where_to_save_each_file: false,
+        remember_last_used_download_directory: true,
         prevents_sleep_while_downloading: true,
         media_cookie_source: MediaCookieSource::default(),
         site_logins: Vec::new(),
@@ -702,6 +703,25 @@ mod tests {
         assert!(!default_settings().auto_add_clipboard_links);
     }
 
+    #[test]
+    fn remembers_last_used_download_directory_by_default() {
+        assert!(default_settings().remember_last_used_download_directory);
+    }
+
+    #[test]
+    fn decodes_disabled_last_used_download_directory_setting() {
+        let stored = json!({
+            "state": {
+                "rememberLastUsedDownloadDirectory": false
+            },
+            "version": 3
+        });
+
+        let settings = decode_stored_settings(&Value::String(stored.to_string())).unwrap();
+
+        assert!(!settings.remember_last_used_download_directory);
+    }
+
     #[test]
     fn ignores_legacy_extension_pairing_token_field() {
         // Older standard installs persisted `extensionPairingToken` as