[Feature] Add xBull wallet support via the WalletAdapter interface

[collinsezedike]

Summary

Implement WalletAdapter (apps/web/src/lib/wallet.ts) for xBull, alongside the existing FreighterWallet. xBull has a mobile app, unlike Freighter, which is desktop-only.

Motivation

The README targets "users in West Africa and other emerging markets" and the roadmap names low-end Android devices as the target device class, but Freighter cannot be installed on mobile at all. xBull is a real path to reaching that user on a phone.

Proposed Solution

Add an XBullWallet class implementing the WalletAdapter interface (isInstalled/isAuthorized/connect/sign) introduced in #476, using xBull's own connection API. Do not wire it into the UI yet, a wallet-picker issue will follow once at least one non-Freighter wallet exists to design the picker against; this issue is just the adapter implementation.

Scope

Field	Value
Area	Frontend
Protocol affected	None
Network	Both
Breaking change?	No

Acceptance Criteria

• XBullWallet implements WalletAdapter fully (isInstalled, isAuthorized, connect, sign)
• Matches the same E2E-mock-wallet short-circuit pattern FreighterWallet uses, so Playwright e2e tests can exercise it without a real extension
• Unit tests covering the real xBull path and the e2e-mock path, mirroring wallet.test.ts's existing Freighter coverage
• pnpm --filter @meridian/web lint && pnpm --filter @meridian/web typecheck && pnpm --filter @meridian/web test pass

Additional Context

Second of the multi-wallet batch. Depends on #476 (merged). Followed by a LOBSTR adapter issue, then a wallet-picker UI issue, then a docs update.

[Chigybillionz]

I can take this up and deliver a fix. Please assign.

Consider me

[karanjadavi]

@karanjadavi has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

can i work on this issue

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[drips-wave]

Congratulations, @karanjadavi! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on August 31, 2026.

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[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox!

@karanjadavi's PR #598 was approved and merged by @collinsezedike.

🏆 @karanjadavi: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (923 total points). Track your full progress on GrantFox.

👏 Great work, @karanjadavi! Keep contributing to drydocs.