Update in-app About copy with the new one-sentence positioning pitch

[christabel888]

Context: Per the pivot doc, the new one-sentence pitch should appear "everywhere," including in-app.

Where:

• Wherever an About/info screen exists (check src/components/SettingsScreen.tsx or a dedicated About screen if one exists)

What to do:

• Update the in-app description to: "Stellar Insights is an open-source analytics platform that turns Stellar blockchain data into actionable ecosystem intelligence through dashboards, rankings, wallet analytics, and Soroban metrics."
• Also update README.md to describe the new dashboard screens and restructured tabs once they exist, as part of this same docs pass.

Suggested approach:

1. Find the app's About/info screen (or SettingsScreen.tsx if there's no dedicated one) and update its description text to the new one-sentence pitch.
2. Also update README.md to describe the new dashboard screens and restructured tabs once Scaffold NetworkDashboardScreen.tsx and useNetworkDashboardScreen.ts hook #21-Update app store screenshots/copy to reflect new IA #41 exist, as part of this same docs pass (folded in from the old Update mobile README.md with new dashboard/nav structure #4).

Watch out for:

• Do this last, after Scaffold NetworkDashboardScreen.tsx and useNetworkDashboardScreen.ts hook #21-Update app store screenshots/copy to reflect new IA #41 actually exist -- a README describing screens that don't exist yet is worse than no README update.

Definition of done:

• In-app About copy uses the new positioning pitch
• README reflects the post-pivot screen/nav structure