🔧 Replace Vite/Vitest with TypeScript 7 and node --test

- Use tsc 7 for build (vite no longer needed for a Node library)
- Use node --test with --experimental-strip-types for tests (vitest dropped)
- Use c8 for coverage instead of vitest's built-in coverage
- Add tsconfig.build.json separating typecheck from emit config
- Drop DOM lib, add strict noUncheckedIndexedAccess/noImplicitOverride
- Pin engines.node to >=22.6 (required for --experimental-strip-types)
- Update CI to Node 24 LTS (unflagged strip-types)
- Add @types/node for node:test / node:assert types

src/vite-env.d.ts

@@ -1 +0,0 @@
-/// <reference types="vite/client" />