[BUG] options.env is still overridden by ~/.claude/settings.json in SDK 0.3.199

## Description

With `@anthropic-ai/claude-agent-sdk@0.3.199`, environment variables passed through
`query({ options: { env } })` can still be overridden by the `env` block in
`~/.claude/settings.json`.

This appears to reproduce the behavior reported in #217 and #215, even though the
SDK changelog states that a related issue was fixed in version 0.2.73.

## Reproduction

Create the following user-level settings file:

`~/.claude/settings.json`

```json
{
"env": {
"ANTHROPIC_API_KEY": "key-from-settings",
"ANTHROPIC_BASE_URL": "https://settings.example.invalid"
}
}
```

Run the SDK with different values in `options.env`:

```typescript
import { query } from "@anthropic-ai/claude-agent-sdk";

for await (const message of query({
prompt: "Hello",
options: {
settingSources: ["user", "project", "local"],
env: {
...process.env,
ANTHROPIC_API_KEY: "key-from-options",
ANTHROPIC_BASE_URL: "https://options.example.invalid"
}
}
})) {
console.log(message);
}
```

## Expected behavior

The spawned Claude Code process should use the values explicitly supplied through
`options.env`:

```text
ANTHROPIC_API_KEY=key-from-options
ANTHROPIC_BASE_URL=https://options.example.invalid
```

## Actual behavior

The spawned Claude Code process uses the values from:

```text
~/.claude/settings.json
```

As a result, the SDK invocation may send requests to the wrong
`ANTHROPIC_BASE_URL` or authenticate with the wrong `ANTHROPIC_API_KEY`.

This is particularly problematic for applications that select credentials and
Anthropic-compatible endpoints dynamically for each request.

## Impact

This behavior prevents SDK applications from reliably selecting a different API key
and base URL per invocation.

It affects, for example:

- Multi-tenant applications with per-request credentials
- Applications that use different Anthropic-compatible providers
- Applications sharing a machine with an interactive Claude Code installation
- Applications that need to preserve the user's global `settings.json` while using
isolated credentials for SDK sessions

## Environment

- `@anthropic-ai/claude-agent-sdk`: `0.3.199`
- OS: Linux
- Runtime: Node.js
- `settingSources`: `["user", "project", "local"]`

## Related issues

- [#217 — Programmatic options.env does not override env values in ~/.claude/settings.json](https://github.com/anthropics/claude-agent-sdk-typescript/issues/217)
- [#215 — ~/.claude/settings.json always takes precedence of query.option.env](https://github.com/anthropics/claude-agent-sdk-typescript/issues/215)
- [#144 — ANTHROPIC_BASE_URL via env option broken in v0.2.8+](https://github.com/anthropics/claude-agent-sdk-typescript/issues/144)

The changelog for SDK `0.2.73` states:

> Fixed `options.env` being overridden by the `~/.claude/settings.json` env block when not using `user` as a `settingSources` option.

However, the behavior is still reproducible with SDK `0.3.199` when the user settings
source is enabled.