feat(plugin): add session HTTP middleware

[rekram1-node]

Summary

• add an Effect-native HTTP execution seam in packages/ai
• expose a normal ctx.session.hook("http", event => event.use(...)) hook in Effect and Promise plugin APIs
• adapt Effect HTTP types to Web types at the Core plugin boundary
• expose raw HTTP statuses before provider error classification, allowing response normalization and retries
• preserve request method, headers, body, response streaming, request attribution, bodyless statuses, cancellation, and middleware error messages
• migrate the built-in OpenAI hook and remove the superseded request-transform API

The HTTP hook currently applies only to native models. The AI SDK path is intentionally unchanged.

Testing

• root bun typecheck across all packages
• bun test test/compile.test.ts test/executor.test.ts in packages/ai
• bun test test/plugin/promise.test.ts test/plugin/provider-openai.test.ts test/session-runner.test.ts test/session-runner-recorded.test.ts in packages/core
• production builds for packages/ai and packages/plugin