Frontend deps: host re-declares packages/ui's dependency set; two headless UI libraries; loose Tailwind floor #521

Tier 3: dependency hygiene

Problem

• host/client_app/package.json re-declares nearly all of packages/ui's runtime dependencies: radix-ui, @base-ui/react, cmdk, recharts, vaul, sonner, input-otp, embla, next-themes, react-day-picker, and others. That gives two lists to keep in sync.
• tailwindcss: "^4.0.0" is a very loose floor next to @tailwindcss/vite.
• autoprefixer and postcss are declared but are probably unused with Tailwind 4's Vite plugin. This needs verifying.
• Two headless-UI foundations are in use: @base-ui/react (1 file) alongside radix-ui (34 files). @radix-ui/react-slot also sits next to the umbrella radix-ui package.

Versions are otherwise current: React 19.2, Vite 8, Vitest 5, Biome 2.5.

Fix

• Make the host depend on @simple-module-py/ui only, and drop the re-declared packages that host code doesn't import directly.
• Raise the Tailwind floor to the version actually in use (^4.3).
• Remove autoprefixer/postcss if nothing loads them.
• Port the single @base-ui/react usage to radix, or the reverse, and keep one library.