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)

package.json

@@ -29,6 +29,7 @@
 		"next-themes": "^0.4.6",
 		"overlayscrollbars": "^2.12.0",
 		"overlayscrollbars-react": "^0.5.6",
+		"posthog-js": "^1.280.1",
 		"react": "19.2.0",
 		"react-dom": "19.2.0",
 		"react-hook-form": "^7.42.1",
@@ -43,6 +44,7 @@
 		"@codecov/vite-plugin": "^1.9.1",
 		"@commitlint/cli": "^19.0.0",
 		"@commitlint/config-conventional": "^19.0.0",
+		"@posthog/nextjs-config": "^1.3.6",
 		"@tailwindcss/postcss": "^4.1.15",
 		"@testing-library/jest-dom": "^6.9.1",
 		"@testing-library/react": "^16.3.0",