build: emit the ESM bundles for ES2018

[stefanoverna]

npm run build printed a wall of esbuild warnings while bundling cma-client-browser:

▲ [WARNING] Top-level "this" will be replaced with undefined since this file is an ECMAScript module

    ../rest-client-utils/dist/esm/pollJobResult.js:1:17:
      1 │ var __awaiter = (this && this.__awaiter) || function (thisArg, _arg...

They were harmless. With target: es2015 TypeScript has to downlevel async/await, object rest and for await…of into its own __awaiter / __rest / __asyncValues helpers, and it emits each one guarded by (this && this.__awaiter) || function (…) {…} so the CommonJS emit can reuse a copy hoisted onto exports. In an ES module top-level this is undefined by spec, so esbuild substituting undefined is exactly right — the guard short-circuits and the inline helper is used.

Rather than silence the warning, this removes its cause: ES2018 has all three constructs natively (async/await landed in ES2017, object rest and for await…of in ES2018), so TypeScript emits no helpers at all and the shipped code is the code we wrote. pollJobResult.js is now a plain export async function, and grep "this && this.__" finds nothing left under any dist/esm.

Eight packages/*/tsconfig.esm.json move to "target": "es2018", each gaining a matching "lib" because the root tsconfig pins es2017 and for await…of needs Symbol.asyncIterator declared. cma-client-analysis is untouched — it runs tsc alone and has no dist/esm.

The CommonJS output and dist/types are byte-identical to before; CJS keeps its ES2015 target, where top-level this is exports and nothing warns. The one consequence for users is that dist/esm now expects an ES2018 runtime — Node 10+, browsers with Symbol.asyncIterator. The bundle in cma-client-browser/esbuild.ts already targeted ES2018, so this makes the rest of the repo consistent with it.

Changeset is minor for the eight packages that build an ESM output.

Test plan

• npm run build — 9/9 tasks green, no esbuild warnings.

https://claude.ai/code/session_01Dw3PG2vUep69n8te7emzyQ