refactor(ui): centralize wallet selection to prevent stale sync panel cache

[lklimek]

Context

PR #642 introduced a platform_sync_info cache on WalletsBalancesScreen to avoid DB reads every frame for the sync status panel. The cache is refreshed in select_hd_wallet() and two display_task_result() handlers.

Problem

Several code paths assign self.selected_wallet directly without going through select_hd_wallet(), which means platform_sync_info is not refreshed:

• update_selected_wallet_for_network() (lines 288, 309) — fallback wallet selection after network switch
• Wallet removal handler (line 716) — selecting next wallet after removing current
• refresh_on_arrival() (line 2239) — auto-selecting first wallet when none selected

This can leave stale sync status data displayed for the wrong wallet.

Proposed Solution

Create a centralized set_selected_hd_wallet(&mut self, wallet: Option<Arc<RwLock<Wallet>>>) helper that:

1. Sets self.selected_wallet
2. Clears self.selected_account
3. Persists the wallet hash
4. Refreshes platform_sync_info cache

Replace all direct assignments to self.selected_wallet with calls to this helper.

References

• PR backport: feat(ui): add sync status panel to wallet screen #642 review comment: https://github.com/dashpay/dash-evo-tool/pull/642/files#r2851751993
• Affected file: src/ui/wallets/wallets_screen/mod.rs

_{🤖 Filed by Claudius the Magnificent AI Agent}