Fix wallet reconnection state loss (Closes #136)

[giftexceed]

Summary

Fixes intermittent loss of application/session state after a wallet reconnect. Investigation traced it to three issues in the dashboard's reconnection flow (dashboard/src/services/wallet.ts + walletStore.ts):

1. Transient failure wiped the saved session. restoreWalletSession() cleared the persisted wallet id on any fetchAddress() failure. A temporary RPC blip, a wallet extension still loading, or a locked account permanently deleted the user's saved wallet, so on the next load they appeared disconnected. The persisted session is now treated as the source of truth — a failed refresh surfaces a recoverable error but keeps the session.
2. Transient null-address updates clobbered a live session. The kit emits intermediate STATE_UPDATED events with no address mid-reconnect; honouring them flipped the UI back to "Connect Wallet". Only the dedicated DISCONNECT event now tears a session down.
3. StrictMode double-invoke race. The restore effect ran twice with no guard, letting two concurrent restores race into clearing each other. Concurrent calls now share a single in-flight promise.

Additional improvements

• Persist the resolved address so the connected UI is restored optimistically on reload (state persists immediately, before the async refresh).
• New isReconnecting state with a "Reconnecting…" button affordance.
• Clear stale errors when starting a connect; disconnectWallet always clears local state without throwing.

Tests

Added integration tests (kit mocked via Jest moduleNameMapper):

• src/services/wallet.test.tsx — successful reconnect, transient-failure keeps session, transient-null guard, disconnect teardown, concurrent-restore coalescing, no-op when no wallet saved.
• src/components/WalletConnectButton.test.tsx — restored-session UI + connected UI surviving a reconnection blip.

import.meta.env was isolated into src/config/stellarNetwork.ts (mapped to a test stub) so the existing Jest runner — which executes modules as CommonJS — keeps working without enabling native ESM (which breaks the jest-axe suites).

Verification

• jest: 31 passed (was 22; +9 new) ✅
• tsc --noEmit: clean ✅
• eslint --max-warnings=0: clean ✅
• vite build: succeeds ✅

Acceptance criteria

• State persists after reconnection
• Wallet reconnects reliably
• Tests pass

Closes #136