fix(VAP-12030): use dynamic import for ESM-only @xenova/transformers

[vapi-tasker]

Summary

Fixes the ERR_REQUIRE_ESM error reported by customers when using the @vapi-ai/mcp-docs-server npm package. The @xenova/transformers package is ESM-only, but TypeScript compiled the static import to require() in CJS output, causing a runtime crash.

• Reconstructed the docs-server TypeScript source from the published npm package into this repo (the original source repo VapiAI/mcp-docs-server is private/inaccessible)
• Changed import { pipeline } from '@xenova/transformers' (static, compiled to require()) to const { pipeline } = await import('@xenova/transformers') (dynamic, works in both CJS and ESM)
• Added 8 tests verifying the fix: compiled output check, import regression test, class construction, and unit tests

Root Cause

@xenova/transformers is an ESM-only package. The docs-server has no "type": "module" in package.json and uses "module": "Node16" in tsconfig, so TypeScript compiles static imports to require(). This causes ERR_REQUIRE_ESM at runtime.

Fix

Use dynamic import() inside the _initialize() method instead of a static top-level import. Dynamic import() works in both CJS and ESM contexts and is preserved by TypeScript's compilation.

Key file: docs-server/src/utils/vector-search.ts line 50

Test Results

All 8 tests pass:

• Compiled output does NOT contain require('@xenova/transformers')
• Compiled output DOES contain import('@xenova/transformers')
• VectorSearch class imports without ERR_REQUIRE_ESM
• VectorSearch instance constructs without crash
• isReady(), getIndexSize(), search(), invalidateIndex() all work correctly

Notes

• The root repo build (npm run build) has pre-existing failures on main (missing @types/node, @types/jest) unrelated to this change
• The docs-server/ subdirectory builds and tests independently with its own tsconfig.json and package.json
• Package version bumped to 0.2.0

Linear: VAP-12030