feat(node-client-sdk): adding support for mobile usage

[joker23]

SDK-2486

This PR will add support for mobile key as a valid credential.

This PR will also harden some typing in the sdk client code.

---

Note

Medium Risk
Changes which LaunchDarkly hosts and paths the SDK hits when useMobileKey is set; default client-side ID behavior is unchanged, with validation blocking hash + mobile key at startup.

Overview
Adds useMobileKey so the Node client can authenticate with a mobile key instead of a client-side ID. When enabled, NodeClient switches to mobile FDv1 endpoints (mobileFdv1Endpoints), sets credentialType to mobileKey, and uses mobile analytics/diagnostic paths (/mobile, /mobile/events/diagnostic) rather than the credential-in-path client-side URLs.

NodeDataManager drops secure-mode hash in mobile key mode (warns and omits the h= query param) so runtime identify() does not throw if a hash is passed. validateOptions rejects configuring hash and useMobileKey together at construction.

Typing is tightened: custom storage is LDStorage, and NodePlatform takes ValidatedOptions for platform-related fields. Tests mock NodePlatform and assert mobile vs default URL and Authorization header behavior for polling, streaming, diagnostics, and events.

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[github-actions]

@launchdarkly/js-sdk-common size report
This is the brotli compressed size of the ESM build.
Compressed size: 26365 bytes
Compressed size limit: 29000
Uncompressed size: 129044 bytes

[github-actions]

@launchdarkly/js-client-sdk-common size report
This is the brotli compressed size of the ESM build.
Compressed size: 38739 bytes
Compressed size limit: 39000
Uncompressed size: 212244 bytes

[github-actions]

@launchdarkly/browser size report
This is the brotli compressed size of the ESM build.
Compressed size: 179579 bytes
Compressed size limit: 200000
Uncompressed size: 831422 bytes

[github-actions]

@launchdarkly/js-client-sdk size report
This is the brotli compressed size of the ESM build.
Compressed size: 31978 bytes
Compressed size limit: 34000
Uncompressed size: 114243 bytes

[joker23]

@cursor review

[cursor]

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.