Add “Watcher” Mode to Monitor Local File Changes

[eliyya]

Description

This PR introduces a new “Watcher” mode under the File > Import menu, allowing users to monitor changes to a selected local file and automatically update the editor and graph.

Motivation

I work a lot with generating JSON files and I use jsoncrack.com a lot to view the generation, but having to re-import the JSON every time it is regenerated really disrupts my workflow. jsoncrack.com is already perfect, but I thought that if the tool had a watch mode it would be much better, so I implemented that option.

Implementation Details

• Added a "Watcher" button in the import modal.

• When activated, the file picker (window.showOpenFilePicker) opens for the user to select a file.
• The selected file is loaded initially, and a setInterval runs every 3 seconds to check for changes using fileHandle.getFile().
• If the file changes, the content is reloaded into the editor, the graph is refreshed and a toast appears.

• A global state is used to manage the watcher and its interval.
• While watcher mode is active:
  • The editor is set to readonly.
  • Format change options and Live Transform are disabled.
• A “Stop Watching” button is available to stop the watcher, clear the interval, and re-enable disabled features.

Benefits

• Allows real-time monitoring and visualization of local files without manual re-import.
• Ideal for workflows where files are generated or updated externally.
• Maintains compatibility with the existing import flow.