refactor: migrate agent system from XML tool calling to OpenAI SDK with native function calling

- Replace custom XML-based tool parsing (XMLToolExecutor) with OpenAI SDK's
  native tool_calls via `openai` npm package (dangerouslyAllowBrowser)
- Consolidate 4 LLM providers (OpenAI, Claude, Gemini, ClaudeOpenRouter)
  into a single OpenAI SDK-based LLMProvider compatible with any
  OpenAI-style API (OpenAI, OpenRouter, Ollama, vLLM)
- Move agentic tool execution loop from ChatBox into AgentCore
- Update Message type to support tool roles, tool_calls, and tool_call_id
- Update system prompt to remove XML formatting instructions (~45% smaller)
- Remove AttemptCompletionTool (replaced by stop_reason detection),
  ThinkTool, and ThinkingTool
- Polish tool descriptions for OpenAI function calling schema compliance
- Normalize base URLs by stripping /chat/completions suffix

src/agent/tools/index.ts

@@ -1,25 +1,19 @@
 // Base tool system
 export { BaseTool } from './BaseTool';
-export type { ToolResult, ToolParameter, ToolDefinition } from './BaseTool';
+export type { ToolResult, ToolParameter, ToolDefinition, OpenAIToolDefinition, OpenAIFunctionParameters } from './BaseTool';
 
 // Specific tools
 import { AddNotesTool } from './AddNotesTool';
 import { RemoveNotesTool } from './RemoveNotesTool';
 import { ReadMusicTool } from './ReadMusicTool';
-import { AttemptCompletionTool } from './AttemptCompletionTool';
-import { ThinkingTool } from './ThinkingTool';
-import { ThinkTool } from './ThinkTool';
 
-export { AddNotesTool, RemoveNotesTool, ReadMusicTool, AttemptCompletionTool, ThinkingTool, ThinkTool };
+export { AddNotesTool, RemoveNotesTool, ReadMusicTool };
 
 // Tool registry for easy access
 export const AVAILABLE_TOOLS = {
   add_notes: AddNotesTool,
   remove_notes: RemoveNotesTool,
   read_music: ReadMusicTool,
-  attempt_completion: AttemptCompletionTool,
-  thinking: ThinkingTool,
-  think: ThinkTool
 } as const;
 
-export type ToolName = keyof typeof AVAILABLE_TOOLS;
+export type ToolName = keyof typeof AVAILABLE_TOOLS;