WIP: Major cleanup - move Attachment to consumers, simplify agent API

- Removed Attachment from agent package (now in web-ui/coding-agent)
- Agent.prompt now takes (text, images?: ImageContent[])
- Removed transports from web-ui (duplicate of agent package)
- Updated coding-agent to use local message types
- Updated mom package for new agent API

Remaining: Fix AgentInterface.ts to compose UserMessageWithAttachments

packages/coding-agent/src/index.ts

@@ -73,7 +73,7 @@ export {
 	isReadToolResult,
 	isWriteToolResult,
 } from "./core/hooks/index.js";
-export { messageTransformer } from "./core/messages.js";
+export { convertToLlm } from "./core/messages.js";
 export { ModelRegistry } from "./core/model-registry.js";
 // SDK for programmatic usage
 export {