Fix TS2305/TS2497: convert Readable import to type-only

[Copilot]

node:stream is a CJS export = module, so named value imports of Readable fail with TS2305 (no exported member) and TS2497 (must reference default export). Since Readable is used solely as a type annotation in readLoop, a value import was never needed.

Changes

• packages/nanoframe/src/main/core.ts: convert value import to import type, drop node: prefix to avoid module-resolution ambiguity under "moduleResolution": "Bundler"

-import { Readable } from 'node:stream'
+import type { Readable } from 'stream'

import type is exempt from TS2497 — TypeScript resolves named types from export = modules without requiring allowSyntheticDefaultImports.