feat: add zdr parameter to OpenRouter chat settings

[chrisclark]

feat: add zdr parameter to OpenRouter chat settings

Summary

Adds the zdr boolean parameter to the OpenRouter chat settings type definition in the AI SDK provider. This parameter enables clients using the AI SDK to restrict routing to only ZDR (Zero Data Retention) endpoints by setting zdr: true in their provider configuration.

This change is part of a coordinated feature implementation across repositories - the main routing logic is implemented in openrouter-web#7637.

Review & Testing Checklist for Human

• Verify the parameter definition matches the implementation in openrouter-web PR #7637
• Test end-to-end that setting zdr: true in AI SDK actually restricts routing to ZDR endpoints
• Confirm the parameter documentation accurately describes the behavior (should only have effect when explicitly set to true)

Notes

• This is a companion PR to the main implementation in openrouter-web
• The change is minimal (just type definition) but should be tested with the full feature
• Requested by @chrisclark in Devin session

[devin-ai-integration]

Original prompt from chris.clark@openrouter.ai

@Devin add a new API parameter `zdr` that is a boolean. If it is set to true, then the request can only get routed to ZDR endpoints. If it is set to any other value, it does nothing.
Thread URL: https://T053YQ6R5TR.slack.com/archives/C07UF9XLTFF/p1757950438770399?thread_ts=1757950438.770399

[devin-ai-integration]

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