Add Export/Import Automata as JSON Feature

[Z-xus]

Environment:

• React + TypeScript
• PNPM-managed project
• DFA visualization and editor component

Description:
Currently, there is no way to persist or transfer DFA configurations. Users should be able to export the automata as a JSON file and import it back into the app to continue editing or share with others.

Expected Behavior:

• Users can export the current DFA/automata as a JSON file.
• Users can import a previously exported JSON file to restore the DFA.
• Imported DFAs should render correctly in the graph editor with all states, transitions, and labels intact.

Acceptance Criteria:

• Export button downloads a valid JSON representation of the DFA.
• Import button accepts a JSON file and correctly recreates the DFA.
• Validation prevents importing invalid or malformed JSON.

Additional Notes:

• JSON format should include states, transitions, start and accept states.
• Consider using TypeScript types/interfaces for DFA structure to ensure type safety.

[teamheaven]

Hi, I'd like to work on this issue. Please assign it to me.