chore: remove _agentConfigInternal and use _agentConfig directly

[jsonbailey]

Summary

• Removes the duplicate _agentConfigInternal private method from LDAIClientImpl
• Replaces its single call site with _agentConfig(key, context, disabledAIConfig, variables, graphKey), correcting the parameter order (graphKey, variables → variables, graphKey)

Test plan

• yarn workspace @launchdarkly/server-sdk-ai lint passes
• yarn workspace @launchdarkly/server-sdk-ai test passes (181 tests)

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Note

Low Risk
Low risk refactor that removes a duplicate private helper and updates a single call site; behavior should remain the same aside from passing graphKey/variables in the correct order.

Overview
Simplifies LDAIClientImpl by deleting the redundant private _agentConfigInternal helper and having agentGraph call _agentConfig directly.

This also fixes the argument ordering for the internal agent-config fetch in agentGraph (passing variables before graphKey) so configs are evaluated with the intended interpolation variables and graph tracking context.

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[github-actions]

@launchdarkly/js-sdk-common size report
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Uncompressed size: 125843 bytes

[github-actions]

@launchdarkly/js-client-sdk size report
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[github-actions]

@launchdarkly/browser size report
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Uncompressed size: 829982 bytes

[github-actions]

@launchdarkly/js-client-sdk-common size report
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Compressed size: 37169 bytes
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Uncompressed size: 204305 bytes