(feat) Add Grid Lines Toggle Feature with Dynamic Icon

[HarK-github]

Description

This PR adds a visual grid lines toggle feature to the Invoice Co-Pilot spreadsheet editor. Users can now easily show/hide grid lines with a single click, with the icon updating dynamically to reflect the current state.

• Added showGrid state to track grid lines visibility
• Created toggleGrid function that calls AppGeneral.toggleGridLinesCSS() and updates state
• Dynamic icon switching - Icon changes between grid (grid visible) and gridOutline (grid hidden) based on current state

Technical Implementation

const [showGrid, setShowGrid] = useState(true);

const toggleGrid = () => {
  const isVisible = AppGeneral.toggleGridLinesCSS();
  setShowGrid(isVisible);
};

// In JSX
<IonIcon 
  icon={showGrid ? grid : gridOutline}
  onClick={toggleGrid}
/>

Testing Performed

• Click toggles grid lines on/off
• Icon changes correctly between grid and gridOutline
• State persists across toggles
• No console errors

Screenshots

Grid Visible	Grid Hidden