## What does this PR do?
Implements an IndexedDB storage adapter for the onboarding store to replace localStorage. This allows storing much larger data (up to 50% of available disk space) compared to localStorage's limited quota, making it suitable for storing base64-encoded images like logos and banners during onboarding. The implementation includes a fallback to localStorage if IndexedDB is unavailable.
Sometimes when you uploaded a large image or banner you get this error. Even if its within the bounds of 10mb (which is what we allow)
## Visual Demo (For contributors especially)
N/A - This is an infrastructure change with no visual component.
## Mandatory Tasks (DO NOT REMOVE)
- [x] I have self-reviewed the code.
- [x] I have updated the developer docs in /docs if this PR makes changes that would require a documentation change. N/A
- [x] I confirm automated tests are in place that prove my fix is effective or that my feature works.
## How should this be tested?
- Test the onboarding flow and verify that data persists between page refreshes
- Test uploading large images during onboarding to ensure they're properly stored
- Test in browsers with IndexedDB disabled to verify the localStorage fallback works correctly
- Verify that the onboarding state is properly maintained when navigating through the onboarding steps
## Checklist
- I have read the [contributing guide](https://github.com/calcom/cal.com/blob/main/CONTRIBUTING.md)
- My code follows the style guidelines of this project
- I have commented my code, particularly in hard-to-understand areas
- I have checked if my changes generate no new warnings
