Feature/light theme

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Thanks to suggestion by @mdube99 to implement a light mode.

I took a different approach to solving this - be integrating with the existing theme toggle, simplifying the current theme implementation down to only light/dark, and using next theme.

Details:

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🎨 Theme Overhaul & UI Polish

Summary
This PR overhauls the application's theming system to introduce a professional Light Mode, standardizes the color palette to a "Professional Blue," and improves the reliability of report exports.

Key Changes

1. Theme Architecture

• Migrated to next-themes for robust binary Light/Dark mode management.
• Removed legacy, unused theme variants ("Teal", "Ember") to simplify maintenance.
• Implemented a strictly typed "Professional Blue" accent (#3b82f6) as the single source of truth for branding, distinct from semantic status colors (Green/Red).

2. UI Polish

• Light Mode: Added a high-contrast Light theme with Slate grays and distinct borders for readability.
• Dark Mode: Refined background to a neutral "Zinc" palette (#09090b) to reduce eye strain.
• Logo: Replaced the generic gradient placeholder with a Shield icon (Lucide) to align with the security domain.
• Charts: Standardized all Recharts (including "Prevention Rate") to use the primary var(--color-accent) for consistency.

3. Bug Fixes

• Export Overflow: Fixed a critical bug where the Attack Matrix PNG export was clipped. Added logic to force containers to min-width: fit-content during capture.
• Fonts: Restored the Geist font injection that was briefly regressed.

4. Documentation

• Updated docs/dev/STYLE.md to reflect the new design tokens and binary theme principles.

Testing

• Verified Light/Dark toggle persistence.
• Verified Attack Matrix exports in both modes.
• Validated chart color consistency in Analytics > Trends.

[initstring]

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