Add agentDir parameter to model config functions and OAuth storage

- loadAndMergeModels(agentDir) - loads models.json from agentDir
- getAvailableModels(agentDir) - uses agentDir for model discovery
- findModel(provider, id, agentDir) - uses agentDir for model lookup
- configureOAuthStorage(agentDir) - configures OAuth to use agentDir/oauth.json
- createAgentSession calls configureOAuthStorage with options.agentDir
- Export configureOAuthStorage from SDK

packages/coding-agent/src/index.ts

@@ -85,11 +85,12 @@ export {
 } from "./core/oauth/index.js";
 // SDK for programmatic usage
 export {
-	allBuiltInTools,
 	type BuildSystemPromptOptions,
 	buildSystemPrompt,
 	type CreateAgentSessionOptions,
 	type CreateAgentSessionResult,
+	// Configuration
+	configureOAuthStorage,
 	// Factory
 	createAgentSession,
 	// Helpers