[FEATURE]: Let tools opt into strict mode

Feature hasn't been suggested before.

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Describe the enhancement you want to request

A tool can't ask for strict mode. session/llm/request.ts hardcodes strict: false for @ai-sdk/openai, @ai-sdk/azure and @ai-sdk/amazon-bedrock/mantle and leaves it unset everywhere else, so there's no way to turn it on where the provider does support it.

The plumbing already exists — strict?: boolean is a documented field on the AI SDK Tool type, @ai-sdk/amazon-bedrock forwards it into toolSpec.strict, and Bedrock's Converse API enforces it. There's also a TODO for this at packages/llm/src/protocols/openai-responses.ts:264.

Concretely: I have a custom .opencode/tool that takes nested objects, and the model keeps sending table instead of tableName. The tool rejects it and the turn is spent on a retry. Strict mode makes those calls unemittable.

Happy to send a PR: strict?: boolean on the tool definition and the tool.definition hook, leaving the existing strict: false override alone.