fix: include timezone offset in all displayed timestamps

All isoDate() functions now output proper ISO 8601 format with timezone
offset (e.g. 2026-02-28T15:30:00-08:00) instead of bare datetime strings.
Also uses 'T' separator per ISO 8601.

closes #116

src/shared/state.js

@@ -23,6 +23,7 @@ const DEFAULT_STATE = {
     hideFraudContracts: true,
     hideDustTransactions: true,
     dustThresholdGwei: 100000,
+    utcTimestamps: false,
     fraudContracts: [],
     tokenHolderCache: {},
 };
@@ -53,6 +54,7 @@ async function saveState() {
         hideFraudContracts: state.hideFraudContracts,
         hideDustTransactions: state.hideDustTransactions,
         dustThresholdGwei: state.dustThresholdGwei,
+        utcTimestamps: state.utcTimestamps,
         fraudContracts: state.fraudContracts,
         tokenHolderCache: state.tokenHolderCache,
         currentView: state.currentView,
@@ -108,6 +110,8 @@ async function loadState() {
             saved.dustThresholdGwei !== undefined
                 ? saved.dustThresholdGwei
                 : 100000;
+        state.utcTimestamps =
+            saved.utcTimestamps !== undefined ? saved.utcTimestamps : false;
         state.fraudContracts = saved.fraudContracts || [];
         state.tokenHolderCache = saved.tokenHolderCache || {};
         state.currentView = saved.currentView || null;