Add a dashboard screenshot to the readme

[Spagero763]

Context

The README has no visual of the dashboard, so newcomers cannot see what the app looks like. See README.md and assets/.

Acceptance criteria

• A current dashboard screenshot is added to the README.

Per CONTRIBUTING.md: one concern, tests required for behaviour changes, contract code stays no_std with typed errors. CI gate: cargo fmt / cargo clippy --all-targets -- -D warnings / cargo test for Rust, npm run build for the sdk/app.

[Ayinkx1]

Hi i would like to work on this issue please assign to me
I can do it perfectly

[k-deejah]

Hi,I can work on this issue

[grantfox-oss]

🦊 GrantFox — @k-deejah has been assigned to this issue as part of the Official Campaign | FWC26 campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #85)
2. Your PR will be reviewed by the tributary-protocol maintainers

Good luck! Track your progress on GrantFox.

[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox as part of the Official Campaign | FWC26 campaign!

@k-deejah's PR #307 was approved and merged by @Spagero763.

🏆 @k-deejah: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (977 total points). Track your full progress on GrantFox.

👏 Great work, @k-deejah! Keep contributing to tributary-protocol.