Add selectable landing page color themes

[esokullu]

Motivation

• Provide brighter alternatives to the default dark landing page by allowing visitors to preview and persist different palettes (Orange, Whitish, Rosy) while keeping Dark as the default.

Description

• Introduced theme variable fallbacks in :root and added body[data-theme="orange"], body[data-theme="whitish"], and body[data-theme="rosy"] palettes to swap colors across the page.
• Replaced hard-coded color/shadow values with CSS variables (e.g. --panel-bg, --accent-hover, --glow-secondary) and updated gradients/backgrounds to use those variables so themes apply consistently.
• Added a small theme switcher UI in the nav (.theme-switcher with .theme-btn) and an inline script that applies the theme and persists the selection to localStorage under webbrain-theme.
• Touched web/index.html layout and responsive rules minimally to accommodate the switcher and ensure theme buttons behave on small screens.

Testing

• Ran git diff --check to ensure no whitespace or patch-format issues, which completed without errors.

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Codex Task

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Project	Deployment	Actions	Updated (UTC)
webbrain	Ready	Preview, Comment	Apr 12, 2026 11:55pm