Add SDK usage examples

12 examples showing increasing levels of customization:
- 01-minimal: all defaults
- 02-custom-model: model and thinking level
- 03-custom-prompt: replace or modify prompt
- 04-skills: discover, filter, merge skills
- 05-tools: built-in tools, custom tools
- 06-hooks: logging, blocking, result modification
- 07-context-files: AGENTS.md files
- 08-slash-commands: file-based commands
- 09-api-keys-and-oauth: API key resolution, OAuth config
- 10-settings: compaction, retry, terminal settings
- 11-sessions: persistence options
- 12-full-control: replace everything

Also exports FileSlashCommand type from index.ts

packages/coding-agent/examples/sdk/02-custom-model.ts

@@ -0,0 +1,36 @@
+/**
+ * Custom Model Selection
+ *
+ * Shows how to select a specific model and thinking level.
+ */
+
+import { createAgentSession, findModel, discoverAvailableModels } from "../../src/index.js";
+
+// Option 1: Find a specific model by provider/id
+const { model: sonnet } = findModel("anthropic", "claude-sonnet-4-20250514");
+if (sonnet) {
+	console.log(`Found model: ${sonnet.provider}/${sonnet.id}`);
+}
+
+// Option 2: Pick from available models (have valid API keys)
+const available = await discoverAvailableModels();
+console.log(
+	"Available models:",
+	available.map((m) => `${m.provider}/${m.id}`),
+);
+
+if (available.length > 0) {
+	const { session } = await createAgentSession({
+		model: available[0],
+		thinkingLevel: "medium", // off, low, medium, high
+	});
+
+	session.subscribe((event) => {
+		if (event.type === "message_update" && event.assistantMessageEvent.type === "text_delta") {
+			process.stdout.write(event.assistantMessageEvent.delta);
+		}
+	});
+
+	await session.prompt("Say hello in one sentence.");
+	console.log();
+}