feat(util): app-wide 24h/12h clock format

Add util::formatClockDateTime/formatClockTime driven by a process-wide flag (setClock12h,
synced from the time_format setting each frame). Switch the primary user-facing timestamp
displays to it — the transaction list, wallet-state tx + banned-peer times, the explorer
block time, and the block-info dialog — so one preference drives every clock.

Log files, export filenames/content, console line prefixes, the market chart axis, and the
worker-thread "last updated" string intentionally stay fixed 24h.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/data/wallet_state.cpp

@@ -3,6 +3,7 @@
 // Released under the GPLv3
 
 #include "wallet_state.h"
+#include "../util/text_format.h"   // util::formatClockDateTime (app-wide 24h/12h clock)
 #include <algorithm>
 #include <ctime>
 #include <sstream>
@@ -44,13 +45,7 @@ int bestSpendableAddressIndex(const std::vector<AddressInfo>& addresses)
 std::string TransactionInfo::getTimeString() const
 {
     if (timestamp == 0) return "Unknown";
-    
-    std::time_t t = static_cast<std::time_t>(timestamp);
-    std::tm* tm = std::localtime(&t);
-    
-    std::stringstream ss;
-    ss << std::put_time(tm, "%Y-%m-%d %H:%M");
-    return ss.str();
+    return util::formatClockDateTime(timestamp);
 }
 
 std::string TransactionInfo::getTypeDisplay() const
@@ -77,13 +72,7 @@ std::string PeerInfo::getConnectionTime() const
 std::string BannedPeer::getBannedUntilString() const
 {
     if (banned_until == 0) return "Never";
-    
-    std::time_t t = static_cast<std::time_t>(banned_until);
-    std::tm* tm = std::localtime(&t);
-    
-    std::stringstream ss;
-    ss << std::put_time(tm, "%Y-%m-%d %H:%M");
-    return ss.str();
+    return util::formatClockDateTime(banned_until);
 }
 
 } // namespace dragonx