chore(dashboard): in-app editor polished inbox preview

[LetItRock]

What changed? Why was the change needed?

In-App Editor polished Inbox preview component. The designs between Inbox preview in the Configure Step Sidebar and the In-App Editor were not consistent, so I had to take a decision on a few things:

• added in the header line between bell and Inbox buttons
• used the font 12px for the subject
• used body color gray

Did also additional improvements:

• Inbox preview skeleton loader
• Collapsible payload with nice animation

Screenshots

https://github.com/user-attachments/assets/bb44daf5-f3a6-4657-b79b-487b6a0b1926

https://github.com/user-attachments/assets/4ccd1c02-9d64-4bbb-a2a2-2f1b96de62d3

[linear[bot]]

NV-4772 🐛 Step Editor - polish the inbox preview component

[netlify[bot]]

✅ Deploy Preview for novu-stg-vite-dashboard-poc ready!

Name	Link
🔨 Latest commit	8f7ce0960cf49ff7ef33eac24027123fab276a86
🔍 Latest deploy log	https://app.netlify.com/sites/novu-stg-vite-dashboard-poc/deploys/6737dd96cceb520008851808
😎 Deploy Preview	https://deploy-preview-7027--novu-stg-vite-dashboard-poc.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site configuration.

[SokratisVidros]

I am merging this so that it's ready for the bug bashing session.