feat: add PostHog telemetry with privacy-focused tracking

Integrate optional PostHog telemetry to track page views, RDAP queries,
user interactions, and errors while maintaining user privacy.

Key features:
- Type-safe event tracking with discriminated unions
- Automatic source map upload for production error tracking
- Privacy protections (query targets excluded from successful lookups)
- Do Not Track (DNT) header support
- Optional telemetry (disabled by default without environment variables)
- Error boundary with automatic error tracking
- Context-based telemetry integration throughout UI components

Environment variables required for telemetry:
- NEXT_PUBLIC_POSTHOG_KEY: PostHog project API key (client-side)
- NEXT_PUBLIC_POSTHOG_HOST: PostHog API endpoint (client-side)
- POSTHOG_PERSONAL_API_KEY: Source map upload key (server-side)

next.config.mjs

@@ -1,4 +1,6 @@
 // @ts-check
+import { withPostHogConfig } from "@posthog/nextjs-config";
+
 /**
  * Run `build` or `dev` with `SKIP_ENV_VALIDATION` to skip env validation.
  * This is especially useful for Docker builds.
@@ -6,11 +8,27 @@
 !process.env.SKIP_ENV_VALIDATION && (await import("./src/env/server.mjs"));
 
 /** @type {import("next").NextConfig} */
-const config = {
+const nextConfig = {
 	reactStrictMode: true,
 	i18n: {
 		locales: ["en"],
 		defaultLocale: "en",
 	},
 };
-export default config;
+
+// PostHog source map configuration
+// Only uploads source maps in production builds when POSTHOG_PERSONAL_API_KEY is set
+const postHogConfig = {
+	personalApiKey: process.env.POSTHOG_PERSONAL_API_KEY || "",
+	envId: "238067", // PostHog project ID for source map correlation
+	host: "https://us.i.posthog.com",
+	sourcemaps: {
+		// Only enable on production builds with API key
+		enabled: process.env.NODE_ENV === "production" && !!process.env.POSTHOG_PERSONAL_API_KEY,
+		project: "rdap",
+		version: process.env.VERCEL_GIT_COMMIT_SHA || "local",
+		deleteAfterUpload: true,
+	},
+};
+
+export default withPostHogConfig(nextConfig, postHogConfig);