Define design system tokens in Tailwind config

[phertyameen]

Issue #91: Define design system tokens in Tailwind config

Category: Theming
Repo: bridgelet (frontend + docs)

Description

Extend tailwind.config.ts with Bridgelet brand tokens: primary color, secondary, error, success, font families, and spacing scale. Remove all ad-hoc hex values from components.

Acceptance Criteria

• Implementation complete
• Tests passing
• Docs updated
• Reviewed and merged