fix: record non-stream usage for provider-native responses

[nguyenha935]

Summary

• Expand non-stream usage extraction to support provider-native response shapes such as Ollama, Kiro, CommandCode, nested OpenAI Responses usage, and nested Gemini usage metadata.
• Estimate missing prompt tokens from the original request when a provider reports output tokens only, preserving an estimated flag for visibility.
• Preserve cache/reasoning usage metadata when saving usage history so Recent Requests and cost accounting have the same token context.

Test Plan

• ./node_modules/.bin/vitest run --config vitest.config.js --reporter=verbose unit/nonstream-usage-extraction.test.js unit/usage-concern.test.js
• npm run build