Migrate agentcore-harness.ts from api-client to AWS SDK typed client

[jesseturner21]

Context

src/cli/aws/agentcore-harness.ts currently uses the hand-rolled api-client.ts HTTP wrapper with manually defined TypeScript interfaces for harness CRUD and invoke operations. Now that harness is GA, @aws-sdk/client-bedrock-agentcore provides fully typed commands and interfaces that stay in sync with the API automatically.

Problem

The local interfaces (BedrockModelConfig, OpenAiModelConfig, GeminiModelConfig, HarnessModelConfiguration) duplicate what the SDK already provides (HarnessBedrockModelConfig, HarnessOpenAiModelConfig, HarnessGeminiModelConfig, HarnessModelConfiguration). This duplication caused the bug fixed in #1287 — a local type drifted out of sync and silently dropped inference parameters.

Proposed Change

Replace the custom HTTP calls in agentcore-harness.ts with SDK commands:

• InvokeHarnessCommand (with event stream handling for streaming)
• CreateHarnessCommand / UpdateHarnessCommand / DeleteHarnessCommand / GetHarnessCommand

This eliminates ~30 lines of local type definitions and removes the risk of type drift with the API.

References

• PR fix(invoke): preserve model maxTokens when overriding model at harness invoke #1287 discussion: fix(invoke): preserve model maxTokens when overriding model at harness invoke #1287 (comment)
• SDK package already in dependencies: @aws-sdk/client-bedrock-agentcore@^3.1020.0