tsconfig: migrate moduleResolution from node to node16

[The-R4V3N]

Background

`moduleResolution: node` (treated as `node10`) is deprecated in TypeScript 6.0 and will stop functioning in TypeScript 7.0.

Currently silenced with `"ignoreDeprecations": "5.0"` in tsconfig.json to avoid a large refactor, but this is a temporary measure.

What needs to happen

Migrating to `node16` (or `nodenext`) requires all relative imports across `src/` to use explicit `.js` file extensions, e.g.:

```ts
// before
import { createSelfTask } from "./self-tasks";

// after
import { createSelfTask } from "./self-tasks.js";
```

This applies to every file in `src/` — roughly 15+ files with multiple imports each.

When to act

Before upgrading to TypeScript 7.0. Monitor TypeScript release notes for the 7.0 timeline.

Labels

tech-debt