Feature: Client design system — color tokens, typography, and theme

[FadyGergesRezk]

Define the visual foundation for the web client: color palette, typography scale, and Tailwind v4 theme configuration. This issue must be resolved before or alongside #43.

Priority: P0

Tasks

• Define the color palette using daisyUI's default theme or customize it in tailwind.config.js using daisyUI's color tokens
• Choose a daisyUI theme (light/dark/auto) or extend with custom color palette using CSS custom properties
• Pick and configure a typeface (e.g. Inter via @fontsource/inter) and register it in Tailwind config as --font-sans
• Establish a typography scale (heading sizes h1–h4, body, caption, mono) using Tailwind utility classes
• Ensure all daisyUI components render using the defined palette and typography
• Dark mode class toggle visually switches the theme

Acceptance criteria

• pnpm build passes with no type errors
• All daisyUI components render using the defined palette (no hardcoded colors)
• Dark mode class toggle visually switches the theme
• Typography scale is applied consistently across heading and body elements
• Theme mode behavior is explicit (persist toggle state or intentionally do not persist)