v2.9.0 - Multi-Theme Engine & Compact UI Overhaul

Highlights in v2.9.0:

• Multi-Theme Engine: Introduced 4 polished themes with zero-latency switching and localStorage persistence:
  • Deep Ocean (Dark Default): Petrol spruce palette with vibrant cyan and mint accents.
  • Midnight Blue (Dark Space): Classic obsidian space navy with royal blue and teal highlights.
  • Lavender Haze (Light Purple): Soft lilac-violet canvas with vibrant purple, fuchsia accents, and deep eggplant text.
  • Amber Warmth (Light Sandstone): Warm sandstone canvas with terracotta orange, amber accents, and dark espresso text.
• Appearance & Theme Settings Panel: Interactive theme switcher cards with live color palette swatches, dark/light mode badges, active checkmark indicators, and toast feedback.
• Card & Layout Compaction: Compacted glass-card padding, overview metric cards, icons, and theme selector grid footprint for a cleaner, higher-density dashboard experience.
• Consolidated Typography Architecture: Centralized font family, weight, and size definitions into CSS custom variables.
• Test Suite & Verification: Added comprehensive unit tests in ThemeSettings.test.tsx covering initial render, click-to-switch behavior, toast messages, legacy alias resolution, and invalid fallback handling (100% test pass rate across 277 backend Pytest tests and 89 frontend Vitest tests).
• Documentation & Screenshots Gallery: Updated README.md with high-resolution theme showcase comparisons and refreshed settings preview.