fix: resolve invisible text in Guide panel during light mode (#395)

[Himanth-reddy]

Description

Resolves Issue #394 #395 where switching the web application / homepage to light mode caused text inside the Guide panel (Setup Roadmap section) and other hardcoded card components to become invisible due to hardcoded dark backgrounds (oklch(0.15...), oklch(0.18...)).

Root Cause

The CSS classes for .guide-card, .compare-row.head .compare-cell, .setup-step, and mobile compare tables used fixed dark backgrounds rather than theme-aware variables. When light mode ([data-theme="light"]) was active, text colors adapted to dark ink (var(--ink)), causing dark text to render over hardcoded dark backgrounds.

Fix

• Updated .guide-card background to use var(--bg-2) so it adapts to white in light theme and dark grey in dark theme.
• Updated .compare-row.head .compare-cell and mobile compare table cells to use var(--bg-3).
• Replaced hardcoded icon and step indicator backgrounds in setup steps with theme variables.

Closes

Closes #395 #395