perf(contracts): reduce clone/storage overhead across all three contr…

[abrak01]

What changed

src/wallet/StellarWalletAdapter.ts (new)
A provider-agnostic WalletAdapter implementation that delegates connect() and
sign() to mobileWalletConnectors, which already handles provider selection
(Freighter on desktop, Albedo on mobile). No provider-specific code lives in
the adapter itself.

src/wallet/index.ts
Swaps the singleton from FreighterAdapter to StellarWalletAdapter.
FreighterAdapter is still exported for back-compat.

src/hooks/useWallet.tsx
disconnect() now delegates to walletAdapter.disconnect() instead of duplicating
the localStorage cleanup inline.

src/components/CreditSection.tsx
handleWithdraw / handleRepay now call walletAdapter.getAddress() first and only
prompt connect() when no address is persisted — avoids an unnecessary popup on
every transaction.

Supported adapter shape

┌───────────┬──────────┐
│ Method │ Behavior │
├───────────┼──────────┤
│ connect() │ Picks Freighter (desktop, extension present) or Albedo │
│ │ (mobile / fallback) │
├───────────┼───────────────────────────────────────────────────────────────┤
│ sign(xdr) │ Signs with whichever provider was used to connect │
├──────────────┼────────────────────────────────────────────────────────────┤
│ getAddress() │ Returns persisted address from localStorage │
├──────────────┼────────────────────────────────────────────────────────────┤
│ disconnect() │ Clears session and redirects to /login │
└──────────────┴────────────────────────────────────────────────────────────┘

Provider-specific limitations

• Freighter requires the browser extension installed and unlocked. If absent on
  desktop, the connector falls back to Albedo automatically.
• Albedo uses a popup/redirect flow — popup blockers can interfere. The
  existing error message already guides the user.
• Network is hardcoded to Testnet in mobileWalletConnectors.ts. Mainnet support
  requires updating that file only.

Proof the existing flow still works

npm run build passes with 0 errors. DepositModal and WalletSetupModal are
unchanged — they use useMobileWallet, which calls the same underlying
connectWallet / signTransactionXdr functions.

Reviewer steps

1. npm run dev
2. Connect with Freighter on desktop → deposit → confirm signing prompt and
   successful transaction.
3. On mobile, connect with Albedo → confirm the Albedo popup appears and
   signing works.

close #46

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