fix: use namespace imports for packages losing default exports on canary

[SisyphusZheng]

Problem

Deno canary CI fails with TS1192: Module has no default export for two npm packages:

File	Import	Error
packages/plugin-tailwindcss/src/mod.ts	import twPostcss from "@tailwindcss/postcss"	TS1192
packages/plugin-vite/src/mod.ts	import prefresh from "@prefresh/vite"	TS1192

The default exports exist at runtime but their .d.ts type declarations lose
the default export signature on canary builds.

Changes

packages/plugin-tailwindcss/src/mod.ts

• import twPostcss from "@tailwindcss/postcss" → import * as twPostcss from "@tailwindcss/postcss"
• wPostcss({...}) → wPostcss.default({...})

packages/plugin-vite/src/mod.ts

• import prefresh from "@prefresh/vite" → import * as prefresh from "@prefresh/vite"
• prefresh({...}) → prefresh.default({...})

Verification

deno task check:types passes on stable Deno v2.7.14.