feat : unify interactive stats and boarders in dark mode (#110)

[YasserYG8]

Title feat: unify interactive states and borders in dark mode (#110)

Description

This PR addresses issue #110 by auditing and unifying interactive states (hover, focus, active) and border styles in dark mode. It ensures high contrast (WCAG AA compliant) and visual polish across the application.

Changes

• Design Tokens: Introduced theme-level design tokens (--color-surface-hover, --color-surface-active, --color-border-dark, and brand hover variants) in globals.css.
• Docs Navigation: Resolved a bug where inactive links turned black (unreadable) on hover in dark mode, and added proper active border styling.
• Workspace UI: Fixed workspace tabs and folder upload buttons from flashing white backgrounds or black text on hover in dark mode.
• Home Layout: Adjusted card grids (Showcase, FAQ, Use Cases, How It Works) and outline buttons to use dark-mode hover backgrounds instead of light-theme flashing.
• Theme Toggle: Added interactive hover background transitions.
• Diagram Nodes: Configured custom selection and hover borders for React Flow nodes.

Verification

• Ran pnpm typecheck (Passed successfully).
• Ran pnpm test (All 66 tests passed successfully).
• Ran pnpm build (Compiled production build successfully).
• Ran pnpm lint (0 errors or warnings).

Related Issues

Closes #110