fix(js-client-sdk): better undefined handling

[joker23]

This PR addresses

SDK-2235
SDK-2236

changes:

• changing isDocument to isWindow because that is more semanitcally correct (we are using window in the conditional block)
• changing bare check to type check (crypto -> typeof crypto !== 'undefined') so that the code doesn't throw due to crypto not existing (this should never happen unless running on some bad obscure browser)

---

Note

Low Risk
Low risk: small guard-condition fixes around window and crypto presence to avoid runtime errors in non-browser/limited environments. Behavior changes only when these globals are missing, where the previous code could throw or incorrectly skip listener registration.

Overview
Fixes environment detection in the browser SDK by gating addWindowEventListener on isWindow() (matching the actual window usage) and updating the no-op comment accordingly.

Hardens UUID v4 generation in both the SDK and browser-telemetry packages by replacing the unsafe crypto truthiness check with typeof crypto !== 'undefined' before calling crypto.getRandomValues, preventing ReferenceErrors when crypto is absent.

^{Reviewed by Cursor Bugbot for commit 3cee041. Bugbot is set up for automated code reviews on this repo. Configure here.}

[joker23]

@cursor review

[github-actions]

@launchdarkly/js-sdk-common size report
This is the brotli compressed size of the ESM build.
Compressed size: 25623 bytes
Compressed size limit: 29000
Uncompressed size: 125843 bytes

[github-actions]

@launchdarkly/browser size report
This is the brotli compressed size of the ESM build.
Compressed size: 179383 bytes
Compressed size limit: 200000
Uncompressed size: 830325 bytes

[github-actions]

@launchdarkly/js-client-sdk-common size report
This is the brotli compressed size of the ESM build.
Compressed size: 37607 bytes
Compressed size limit: 38000
Uncompressed size: 207149 bytes

[github-actions]

@launchdarkly/js-client-sdk size report
This is the brotli compressed size of the ESM build.
Compressed size: 31721 bytes
Compressed size limit: 34000
Uncompressed size: 113136 bytes

[cursor]

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^{Reviewed by Cursor Bugbot for commit 23fc8f9. Configure here.}