⚡ Bolt: [performance improvement] Optimize LazyVerticalGrid items composition

[LeanBitLab]

💡 What: Replaced items + indexOf with itemsIndexed in LazyVerticalGrid.
🎯 Why: Calling indexOf(item) on the list during the composition of each item is an $O(N)$ operation per visible item, which can degrade scrolling performance causing frame drops as the list grows. Changing items to itemsIndexed provides the index in $O(1)$ time, directly fixing the bottleneck. Also fixed a duplicate import that broke compilation during the process.
📊 Impact: Prevents O(N) lookup for every visible item during composition.
🔬 Measurement: Scrolling through large feed lists will be noticeably smoother with fewer dropped frames.

---

PR created automatically by Jules for task 17786583940623483941 started by @LeanBitLab

[google-labs-jules]

👋 Jules, reporting for duty! I'm here to lend a hand with this pull request.

When you start a review, I'll add a 👀 emoji to each comment to let you know I've read it. I'll focus on feedback directed at me and will do my best to stay out of conversations between you and other bots or reviewers to keep the noise down.

I'll push a commit with your requested changes shortly after. Please note there might be a delay between these steps, but rest assured I'm on the job!

For more direct control, you can switch me to Reactive Mode. When this mode is on, I will only act on comments where you specifically mention me with @jules. You can find this option in the Pull Request section of your global Jules UI settings. You can always switch back!

New to Jules? Learn more at jules.google/docs.

---

For security, I will only act on instructions from the user who triggered this task.