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/agent/src/types.ts

@@ -151,7 +151,7 @@ export interface AgentTool<TParameters extends TSchema = TSchema, TDetails = any
 // AgentContext is like Context but uses AgentTool
 export interface AgentContext {
 	systemPrompt: string;
-	messages: Message[];
+	messages: AgentMessage[];
 	tools?: AgentTool<any>[];
 }