Add error handling for localStorage operations

[avinxshKD]

I was testing the app in private browsing mode and it crashes immediately when trying to save graphs. Turns out all the localStorage calls in src/graph-builder/local-storage-manager.js and src/component/fileBrowser.jsx have zero error handling.

Lines like:

window.localStorage.setItem(this.ALL_GRAPHS, window.btoa(JSON.stringify(Array.from(this.allgs))));

Just throw and kill the app when localStorage is disabled or quota exceeded. No try-catch, no fallback, nothing.

Would be good to wrap these in try-catch blocks and either:

1. Show a toast notification that persistence is unavailable
2. Fall back to in-memory storage for the session
3. Both

Similar to how the Axios error handling works elsewhere in the codebase.

[avinxshKD]

let me know what do you think, working on the fix thanks @pradeeban