Fix default Kiro tool input schema when parameters missing

[Darley-Wey]

Motivation

• Requests that include tools without a parameters field caused Kiro to receive an invalid/malformed tool schema and return 400 errors, so tools must always supply a valid input schema.

Description

• Add ensureKiroInputSchema(parameters interface{}) interface{} to provide a default empty object schema when parameters is missing or null.
• Use the new helper in internal/translator/kiro/openai/kiro_openai_request.go within convertOpenAIToolsToKiro to normalize parameters before building the KiroToolSpecification.
• Apply the same defaulting in internal/translator/kiro/openai/kiro_openai.go in ConvertOpenAIToolsToKiroFormat so both conversion paths produce a valid InputSchema.

Testing

• Ran go test ./internal/translator/kiro/openai and the package tests completed successfully (ok).

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Codex Task