refactor: vendor pretext core for publishable cutover

[Huxpro]

Summary

• replace the local forked core entrypoint with a vendored upstream pretext core bound through createPretext({ measurement: lynxMeasurementHost })
• keep Lynx-specific runtime shims and measurement host local, while letting native and web examples share the same core layout logic
• add web environments for the examples and keep the basic demos working with explicit Web fallbacks where they directly call lynx.getTextInfo

Why

We want lynx-pretext to converge on upstream pretext instead of maintaining a long-lived fork, but we still need a publishable package before the upstream changes land and release. This PR vendors the minimal upstream core as a temporary bridge.

Upstream follow-ups:

• feat: add measurement host config entrypoint chenglou/pretext#72
• feat: add a compat entrypoint for portable regex support chenglou/pretext#71

Test Plan

• bun test packages/lynx-pretext/src/layout.test.mjs
• pnpm --filter @lynx-pretext-example/basic exec tsc --project ../../packages/lynx-pretext/tsconfig.json
• pnpm --filter @lynx-pretext-example/basic exec tsc --project tsconfig.json
• pnpm --filter @lynx-pretext-example/basic exec rspeedy build
• pnpm --filter @lynx-pretext-example/basic exec rspeedy build --environment web
• pnpm --filter @lynx-pretext-example/editorial exec rspeedy build --environment web
• pnpm --filter @lynx-pretext/example-dance exec rspeedy build --environment web
• pnpm --filter @lynx-pretext-example/ascii-arts exec rspeedy build --environment web
• pnpm --filter @lynx-pretext-example/dynamic-layout exec rspeedy build --environment web
• pnpm --filter @lynx-pretext-example/bubble exec rspeedy build --environment web

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Project	Deployment	Actions	Updated (UTC)
lynx-pretext	Ready	Preview, Comment	Apr 1, 2026 4:48am