Prevent silent unit/integration test misclassification via positive manifest (#1307 follow-up)

[cliffhall]

Background

#1307 added a new `integration` vitest project for v1.5-ported tests that need node env + 30s timeouts. Membership is controlled by an explicit `integrationTests` array in `clients/web/vite.config.ts`:

```ts
const integrationTests = [
'clients/web/src/test/core/inspectorClient.test.ts',
...
];

projects: [
{ name: 'unit', include: ['clients/web/src/**/*.test.{ts,tsx}'], exclude: integrationTests },
{ name: 'integration', include: integrationTests },
]
```

A new test file under `src/test/core/` that isn't added to `integrationTests` silently falls into the unit project and runs under happy-dom. There's a comment acknowledging this, but it's a sharp edge: an integration-style test that should spawn a real server will fail (or pass for the wrong reasons) under happy-dom with no signal at authoring time.

Proposed change

Flip the manifest so the project that runs is determined by file location rather than enumeration:

```ts
{ name: 'unit', include: ['clients/web/src//*.test.{ts,tsx}'], exclude: ['clients/web/src/test/integration/'] },
{ name: 'integration', include: ['clients/web/src/test/integration/**/*.test.ts'] },
```

This means either:

A) Move the 13 integration tests under a dedicated `src/test/integration/` folder (with sub-paths mirroring source layout) and drop the explicit `integrationTests` array. Cleanest, but it's a 13-file rename + import-path audit.

B) Keep tests where they are, add a per-file marker (e.g. a regex on the first line — `/* @vitest-environment node */`) and have the integration project glob with a filter. More plumbing, less file movement.

Recommend (A) — the rename is mechanical and the layout becomes self-documenting.

Why

• Removes the developer trap entirely — there's no way to add a node-env test that accidentally runs under happy-dom (or vice versa).
• The `integrationTests` array would no longer drift from reality silently.
• Layout matches how most monorepos disambiguate test scopes (`unit/`, `integration/`, `e2e/`).

Acceptance criteria

• Integration tests live in a path that the integration project's `include` glob owns, and unit's `include` excludes (no explicit enumeration).
• Adding a new file under `src/test/integration/` automatically runs in node env; adding one outside automatically runs in happy-dom.
• `npm run test:integration` and `npm run test:coverage` still pass with the same 13 files / 298 tests.
• tsconfig.test.json `include` paths updated to match.

Out of scope

• Renaming the unit-test directory structure or introducing a third project.
• Changing what counts as "integration" — same 13 files in scope.

Origin

PR #1312 review comment (observation #5).