fix: properly serialize error objects in PostHog tracking (#709)

Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

Author: vrcprl

.changeset/fix-error-serialization.md

@@ -0,0 +1,5 @@
+---
+"lingo.dev": patch
+---
+
+Fix error tracking in PostHog by properly serializing error objects

packages/cli/src/cli/utils/observability.ts

@@ -7,6 +7,20 @@ export default async function trackEvent(distinctId: string, event: string, prop
   }
 
   try {
+    const safeProperties = properties ? JSON.parse(JSON.stringify(
+      properties,
+      (key, value) => {
+        if (value instanceof Error) {
+          return {
+            name: value.name,
+            message: value.message,
+            stack: value.stack,
+          };
+        }
+        return value;
+      }
+    )) : {};
+
     const posthog = new PostHog("phc_eR0iSoQufBxNY36k0f0T15UvHJdTfHlh8rJcxsfhfXk", {
       host: "https://eu.i.posthog.com",
       flushAt: 1,
@@ -17,7 +31,7 @@ export default async function trackEvent(distinctId: string, event: string, prop
       distinctId,
       event,
       properties: {
-        ...properties,
+        ...safeProperties,
         meta: {
           version: process.env.npm_package_version,
           isCi: process.env.CI === "true",