Refactor config loading (in progress 3)

src/config/posthog.schema.ts

@@ -0,0 +1,15 @@
+import { z } from 'zod';
+import { CommonConfigSchema } from './common.schema.js';
+
+/**
+ * PostHog configuration options schema
+ */
+export const PostHogConfigSchema = CommonConfigSchema.extend({
+	apiKey: z.string().describe('PostHog API key'),
+	host: z
+		.string()
+		.default('https://app.posthog.com')
+		.describe('PostHog host URL'),
+});
+
+export type PostHogConfigType = z.infer<typeof PostHogConfigSchema>;