fix(sponsor-wallet): align live error status, cross-tab wallet logout and address reconciliation (#269, #270, #283)

[ghzhost]

Summary of Changes

This PR resolves three interconnected sponsor and wallet UX/consistency issues:

1. Sponsor Dashboard Live Error Handling (SponsorDashboardPage sets isLive(false) on a genuine fetch error, showing a misleading "Demo data" badge and "sign in with GitHub" prompt to an already-signed-in sponsor #269):

   • In src/app/dashboard/sponsor/page.tsx, set setIsLive(true) on API fetch failure matching ContributorDashboardPage so signed-in sponsors seeing a live network failure are not incorrectly shown "Demo data" / "Sign in with GitHub".

2. Cross-Tab Wallet State Cleanup on Logout (WalletContext never reacts to a cross-tab logout, so a wallet stays shown as "connected" and usable in a tab where the user was just signed out from another tab #270):

   • In src/context/WalletContext.tsx, added a cleanup effect that invokes disconnect() when user becomes null while a local address remains connected, ensuring signed-out states immediately clear stored wallet credentials across sessions and tabs.

3. Stellar Address Mismatch Warning Affordance (Nothing reconciles WalletContext's connected address against AuthUser.stellarAddress, so the UI can show a wallet as "connected" that differs from the actual payout address on file #283):

   • In src/app/connect/ConnectPanel.tsx, added address reconciliation between the connected browser wallet (WalletContext.address) and registered payout address (AuthUser.stellarAddress), displaying an accessible contextual warning when they differ.

Closes #269
Closes #270
Closes #283

[vercel]

Someone is attempting to deploy a commit to the chonilius' projects Team on Vercel.

A member of the Team first needs to authorize it.