מעצב גלובלי ל-Shadcn UI

# Shadcn Identity Overhaul
I want to completely restyle my Shadcn UI definitions in 'globals.css' and 'tailwind.config.ts' to match a highly premium, 'Dark Mode SaaS' aesthetic (think Linear or Vercel style).
1. Define deep, cool dark background variables (e.g. #0A0A0A) and vibrant primary colors (e.g. Neon Violet / Cyan).
2. Adjust the border-radius variables to make cards razor sharp ('0px') or slightly rounded ('0.5rem') uniformly.
3. Provide the entire updated 'globals.css' and standard button class overrides.
4. Add custom subtle shadows and micro-borders using Tailwind tokens.