Add SDK for programmatic AgentSession usage

- Add src/core/sdk.ts with createAgentSession() factory and discovery functions
- Update loaders to accept cwd/agentDir parameters (skills, hooks, custom-tools, slash-commands, system-prompt)
- Export SDK from package index

Addresses #272

packages/coding-agent/src/core/tools/index.ts

@@ -1,3 +1,5 @@
+import type { AgentTool } from "@mariozechner/pi-ai";
+
 export { type BashToolDetails, bashTool } from "./bash.js";
 export { editTool } from "./edit.js";
 export { type FindToolDetails, findTool } from "./find.js";
@@ -15,8 +17,14 @@ import { lsTool } from "./ls.js";
 import { readTool } from "./read.js";
 import { writeTool } from "./write.js";
 
+/** Tool type (AgentTool from pi-ai) */
+export type Tool = AgentTool<any>;
+
 // Default tools for full access mode
-export const codingTools = [readTool, bashTool, editTool, writeTool];
+export const codingTools: Tool[] = [readTool, bashTool, editTool, writeTool];
+
+// Read-only tools for exploration without modification
+export const readOnlyTools: Tool[] = [readTool, grepTool, findTool, lsTool];
 
 // All available tools (including read-only exploration tools)
 export const allTools = {