Add Glass Theme CSS variables and styles for dock and windows

[YamanAddas]

Motivation

• Provide a premium "Glass Theme" look using glassmorphism for OS surfaces (windows and dock) with strong blur, subtle borders, and deep shadows.
• Ensure the dock floats bottom-center with a rounded pill shape and smooth hover/magnification for icons.
• Make window frames and headers consistent with thin white borders, deep shadows, and a clean sans-serif typographic base.

Description

• Added new theme variables in css/main.css: --glass-window-bg, --glass-dock-bg, --glass-header-bg, --glass-highlight, and --shadow-strong, and mirrored them in the light theme overrides.
• Implemented .dock-container styles that float centered at the bottom with backdrop-filter: blur(20px), pill border-radius: 24px, semi-transparent background, subtle border, deep shadow, and hover scaling for .dock-item / .dock-icon.
• Implemented .window-frame styles with 1px solid rgba(255,255,255,0.2) borders, var(--radius-lg) radius, backdrop-filter: blur(20px), box-shadow: var(--shadow-strong), overflow: hidden, and system sans-serif typography.
• Implemented .window-header styles with semi-transparent header background, bottom border, blur, spacing, and sans-serif typography.

Testing

• Served the app locally with python -m http.server and loaded index.html to validate CSS applied in-browser.
• Captured a visual verification screenshot using Playwright saved as an artifact (artifacts/glass-theme.png) to confirm the dock and window surfaces render with the intended blur, borders, shadows, and hover effects.
• Committed the change (css/main.css) successfully; no automated test failures occurred for this CSS-only change.

---

Codex Task