accounts list: use available balance, show blocked amount as secondary line

BML CASA rows on the accounts list were showing currentBalance (the
working/ledger balance, which includes blocked funds). Every other
balance display in the app — transfer screen, contact picker, QR pay,
dashboard totals — uses availableBalance, so the same account was
showing a different figure depending on where you looked at it.

This switches the accounts list to availableBalance for consistency,
and adds a small muted "MVR X.XX blocked" line beneath the balance
when blocked > 0 so the blocked funds are still visible at a glance.
Only BML reports a non-zero blocked amount; MIB and Fahipay rows are
unaffected.

The per-account history page header is untouched — its three-column
Available / Balance / Blocked breakdown still works as before.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/src/main/res/values/strings.xml

@@ -209,6 +209,7 @@
     <string name="accounts">Accounts</string>
     <string name="cards">Cards</string>
     <string name="available_balance">Available Balance</string>
+    <string name="account_blocked_label">%1$s blocked</string>
 
     <!-- Transfer -->
     <string name="transfer_tab_quick">Quick Transfer</string>