The Spotlight configuration logic had a precedence bug where when
'spotlight: true' was set AND the 'SENTRY_SPOTLIGHT' env var contained
a URL string, the SDK would use 'true' instead of the URL from the env var.

According to the Spotlight specification, when 'spotlight: true' is set
and the env var contains a URL, the URL should be used.

Changes:
- Fixed precedence logic in getClientOptions() to properly handle the
  case where config is 'true' and env var is a URL string
- Added 12 comprehensive test cases covering all precedence scenarios
- Reused existing envToBool() utility for env var parsing

Fixes the issue where developers couldn't override the Spotlight URL
via environment variable when using 'spotlight: true' in config.

Before submitting a pull request, please take a look at our

[Contributing](https://github.com/getsentry/sentry-javascript/blob/master/CONTRIBUTING.md)
guidelines and verify:

- [x] If you've added code that should be tested, please add tests.
- [x] Ensure your code lints and the test suite passes (`yarn lint`) &
(`yarn test`).

Fixes a test failure where `process.env.SENTRY_SPOTLIGHT` was not
cleaned up after a test, causing environment variable pollution for
subsequent tests.

The failing test expected `spotlight: true` to resolve to `true`, but
due to the lingering environment variable, it received the URL from
`SENTRY_SPOTLIGHT` instead.

This PR adds an `afterEach` hook to the `spotlight configuration`
describe block to ensure `process.env.SENTRY_SPOTLIGHT` is deleted after
each test, preventing cross-test contamination.

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Co-authored-by: Cursor Agent <[email protected]>