fix: stop dashboard sidebar infinite refetch loop (#2564)

## Summary
- Fix infinite refetch loop in the dashboard sidebar that fires hundreds
of POST+GET requests per second
- The `subscriptionFetchRef` was reset in `finally()`, allowing
re-entrancy: fetch → `setSubscription` → re-render → ref is `false` →
fetch again → infinite loop
- Move the ref reset to the effect cleanup function so it only resets
when `mode` actually changes

## Note: Auth0 favicon 404
The Auth0 login page at `codeflash-ai.us.auth0.com` returns a 404 for
`/favicon.ico`. This is configured in **Auth0 Dashboard > Branding >
Universal Login**, not in application code. Upload the Codeflash favicon
there to resolve.

## Test plan
- [ ] Navigate to dashboard, open Network tab — confirm no repeated
POST/GET polling
- [ ] Switch between personal/org mode — confirm subscription data still
loads correctly
- [ ] Verify sidebar subscription usage display still renders

js/cf-webapp/src/components/dashboard/sidebar.tsx

@@ -106,8 +106,10 @@ export function Sidebar({ className, user, isLoading, error }: SidebarProps): JS
     if (subscriptionFetchRef.current) return
     subscriptionFetchRef.current = true
 
+    let cancelled = false
     getCurrentUserSubscriptionData()
       .then(data => {
+        if (cancelled) return
         if (data) {
           setSubscription({
             optimizations_used: data.optimizations_used || 0,
@@ -117,10 +119,14 @@ export function Sidebar({ className, user, isLoading, error }: SidebarProps): JS
           setSubscription(null)
         }
       })
-      .catch(() => setSubscription(null))
-      .finally(() => {
-        subscriptionFetchRef.current = false
+      .catch(() => {
+        if (!cancelled) setSubscription(null)
       })
+
+    return () => {
+      cancelled = true
+      subscriptionFetchRef.current = false
+    }
   }, [mode])
 
   const toggleTheme = () => {