fix(posthog): disable exception autocapture to stay within free tier

Error tracking exceeded 100K free tier limit (188K in 5 days).

Top exceptions were mostly noise:
- ProviderModelNotFoundError: 75K (user config issues)
- EPIPE/EOF/stream destroyed: 40K (normal pipe closures)
- ENOSPC: 3K (user disk space issues)

Manual captureException() for critical errors in runner.ts
is preserved. Only automatic unhandled exception capture is
disabled.

src/shared/posthog.ts

@@ -155,7 +155,7 @@ export function getPostHogDistinctId(): string {
 
 export function createCliPostHog(): PostHogClient {
   return createPostHogClient("cli", {
-    enableExceptionAutocapture: true,
+    enableExceptionAutocapture: false,
     flushAt: 1,
     flushInterval: 0,
   })
@@ -163,7 +163,7 @@ export function createCliPostHog(): PostHogClient {
 
 export function createPluginPostHog(): PostHogClient {
   return createPostHogClient("plugin", {
-    enableExceptionAutocapture: true,
+    enableExceptionAutocapture: false,
     flushAt: 1,
     flushInterval: 0,
   })