fix(sdk): make the published build importable from plain Node.js

[kosuke55]

Problem

The package ships "type": "module" and the README documents it for headless tooling, but importing it from plain Node.js fails:

$ node -e "import('@drawtonomy/sdk')"
Error [ERR_MODULE_NOT_FOUND]: Cannot find module '.../dist/types'
    imported from .../dist/index.js

So node script.mjs, CLI tools and CI scripts cannot use the SDK at all today — only bundler-based consumers can.

Cause

tsconfig.json used moduleResolution: "bundler". That mode permits extensionless relative imports and emits them verbatim:

// dist/index.js (before)
export * from './types';

Bundlers resolve those, but Node's ESM loader requires explicit file extensions. 45 such specifiers were emitted across dist/. The existing test suite stayed green because Vite rewrites imports in-process, so nothing surfaced the breakage.

Fix

Change	Detail
tsconfig.json	module / moduleResolution: bundler → NodeNext, so the compiler enforces Node's ESM rules at build time
15 source files	added .js to relative imports (mechanical)
src/index.ts	directory import './exporter' → './exporter/index.js'

No source logic and no public API changed. Bundler consumers are unaffected.

Verification

Ran against the built dist/ with plain Node (no bundler):

plain node import      : OK (24 exports, exporter 37)
exportToOpenDrive      : 1458 bytes, roads=1, width=2.999400
exportToLanelet2       : 1258 bytes
exportToOpenScenario   : 1841 bytes, entities=1
parse + odrToShapes    : lanes=1 linestrings=2 points=20

That covers the full headless cycle: createLaneWithBoundaries → createSnapshot → each exporter, plus a parseOpenDriveXml → odrToShapes round-trip that recovers the lane with the correct 2.9994 m width.

Existing suite: 323 passed, 4 skipped.

Regression guard

Added __tests__/nodeEsmResolution.test.ts. It spawns a real Node process against dist/ and runs a generate + export + round-trip cycle.

An in-process test cannot catch this class of bug, because Vite rewrites the specifiers before Node ever sees them — which is exactly why the original breakage went unnoticed. The test skips when dist/ is absent, so it does not require a build to be present.

I verified the guard actually detects the problem: removing the extension from a single import in dist/index.js makes it fail with ERR_MODULE_NOT_FOUND.