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/components/SettingsView.tsx

@@ -1069,6 +1069,21 @@ runEngineChecks(false);
                 </label>
               </div>
 
+              <div className="mac-settings-group">
+                <label className="mac-settings-row cursor-default">
+                  <div>
+                    <span className="text-[13px] text-text-primary">{t($ => $.settings.locations.rememberLastUsedDownloadDirectory)}</span>
+                    <p className="mt-0.5 text-[11px] text-text-muted">{t($ => $.settings.locations.rememberLastUsedDownloadDirectoryDescription)}</p>
+                  </div>
+                  <input
+                    type="checkbox"
+                    checked={settings.rememberLastUsedDownloadDirectory}
+                    onChange={(e) => settings.setRememberLastUsedDownloadDirectory(e.target.checked)}
+                    className="mac-switch"
+                  />
+                </label>
+              </div>
+
               <div className="mac-settings-group">
                 <label className="mac-settings-row cursor-default">
                   <div>