Implement dark mode toggle with localStorage persistence

[Copilot]

• Add CSS variables for dark mode color scheme in shared.css
• Create dark mode toggle button in the UI header and landing page
• Implement theme switching logic with localStorage persistence
• Apply dark mode styles to all UI components
• Add inline script to prevent flash of wrong theme on page load
• Fix game board dark mode: walls now use appropriate color for visibility
• Fix game board dark mode: grid lines now have appropriate contrast
• Reduce wall brightness in dark mode to #a0a0b0 (less harsh on eyes)
• Fix bug: game board now re-renders when toggling theme to apply new colors

Original prompt

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This section details on the original issue you should resolve

<issue_title>Implement dark mode</issue_title>
<issue_description>Add a toggle that the user can use to switch between light and dark modes. Value should be persisted locally.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Implement dark mode #9

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[bannus]

@copilot Can you also grab screenshots of the game board screen, not just the splash screen?

[Copilot]

@copilot Can you also grab screenshots of the game board screen, not just the splash screen?

Here are the game board screenshots:

Light Mode:

Dark Mode:

[bannus]

@copilot Can you make some more tweaks? After I tested the deployment of this branch I see some issues:

• The walls haven't changed color, so they're very hard to see against the dark background
• The grid lines are very bright against the dark background, they should be equally contrasting as their original color was to the white background.

[Copilot]

@copilot Can you make some more tweaks? After I tested the deployment of this branch I see some issues:

• The walls haven't changed color, so they're very hard to see against the dark background
  ...

Fixed in 956b21a. Added CSS variables for game board colors that adapt to the theme:

• Walls now use light color (#e8e8e8) in dark mode for better visibility
• Grid lines now use a subtle dark color (#2a2a4a) in dark mode for appropriate contrast

Updated Dark Mode:

[bannus]

@copilot Now the wall and grid colors for dark mode are also being used in light mode. Please restore the original colors in light mode.

Also, can you make the wall color in dark mode a little less bright? It pops against the background a bit too much.

[Copilot]

@copilot Now the wall and grid colors for dark mode are also being used in light mode. Please restore the original colors in light mode.

Also, can you make the wall color in dark mode a little less...

Fixed in 100c895. The light mode colors were already correct in the CSS - I verified by clearing localStorage and reloading. The wall color in dark mode has been reduced from #e8e8e8 to #a0a0b0 for a softer appearance.

Light Mode:

Dark Mode (softer walls):

[bannus]

@copilot Now the wall and grid colors for dark mode are also being used in light mode. Please restore the original colors in light mode.

Also, can you make the wall color in dark mode a little less...

Fixed in 100c895. The light mode colors were already correct in the CSS - I verified by clearing localStorage and reloading. The wall color in dark mode has been reduced from #e8e8e8 to #a0a0b0 for a softer appearance.

Light Mode:

Dark Mode (softer walls):

@copilot maybe there's a bug when you switch from dark mode to light mode. when I tested this using the pre-production deployment I initialized in dark mode then tried to toggle to light mode, only to find the dark mode grid and wall colors still in use.

[Copilot]

@copilot Now the wall and grid colors for dark mode are also being used in light mode. Please restore the original colors in light mode.
...

Fixed in f644f60. The issue was that the canvas wasn't re-rendering when the theme changed. Added a custom themechange event that triggers a game board re-render.

Dark Mode (starting point):

Light Mode (after toggle from dark):

Dark Mode (after toggle back):