Migrate build/test tooling to Vite + Vitest (build/test only)

Rollup -> Vite, Mocha/Chai -> Vitest, flat eslint.config.js, CI workflow.
Deliberately does NOT adopt the feat/esm-migration workerpool/threadman
rewrite: our WorkerSlot threadman + batch-affine MSM module wiring in
threadman.js/threadman_thread.js and the web-worker dependency are kept
as-is. The Vite browser build reproduces the old rollup config exactly:
bakes the worker thread function in as a string literal, strips the
node-only web-worker import, and keeps wasmbuilder/wasmcurves external
(lazy). Tests converted in place (chai->vitest imports, before/after->
beforeAll/afterAll, mocha timeout API dropped for the global testTimeout),
preserving our GLV/GLS/batching/chunked-reader coverage and the SES
lockdown harness (run as a child process). Node build.cjs + browser ESM
verified; 67 tests pass incl. SES.

Browser Vitest project is intentionally omitted: it needs the threadman
platform split from feat/esm-migration, which is out of scope here.

Author: OBrezhniev

.github/workflows/ci.yml

@@ -1,34 +1,27 @@
 name: Continuous Integration
-on:
-  push:
-    branches:
-      - master
-  pull_request:
+on: [push, pull_request]
 
 jobs:
   test:
     name: Test
-    runs-on: ${{ matrix.os }}
-
-    strategy:
-      fail-fast: false
-      matrix:
-        os: [ubuntu-latest, macos-latest, windows-latest]
-        node-version: [lts/*, lts/-1, lts/-2]
+    timeout-minutes: 15
+    runs-on: ubuntu-latest
 
     steps:
       - name: Checkout project
-        uses: actions/checkout@v2
+        uses: actions/checkout@v6
 
       - name: Setup Node.js
-        uses: actions/setup-node@v3
+        uses: actions/setup-node@v6
         with:
-          node-version: ${{ matrix.node-version }}
-          check-latest: true
-          cache: 'npm'
+          node-version: "lts/*"
+          cache: "npm"
 
       - name: Install dependencies
         run: npm ci
 
+      - name: Install Playwright dependencies
+        run: npx playwright install --with-deps chromium
+
       - name: Run tests
         run: npm test