feat: show relative time on reset dates and billing period duration

Feat: _relativeTime() helper returns human-friendly countdown like
(in 6d 16h), (in 3h 17m), or (in 45m).

Billing Period line now shows total days:  2026-07-26 to 2026-08-26 (31 days)

5-Hour and Weekly reset lines now show countdown:
  Resets at: 2026-07-26 21:06  (in 3h 17m)
  Resets at: 2026-08-02 10:00  (in 6d 16h)

Author: Khip01

lib/src/tui/app.dart

@@ -833,7 +833,7 @@ class AppState extends State<CmdBridgeApp> {
             rows.add(Padding(
               padding: EdgeInsets.symmetric(vertical: 0),
               child: Column(crossAxisAlignment: CrossAxisAlignment.start, children: [
-                Text('  ${_fmtDate(periodStart)}  to  ${_fmtDate(periodEnd)}', style: TextStyle(color: Colors.grey)),
+                Text('  ${_fmtDate(periodStart)}  to  ${_fmtDate(periodEnd)}  ($totalDays days)', style: TextStyle(color: Colors.grey)),
                 SizedBox(height: 1),
                 _bar(periodPct, Colors.blue, label: '${elapsedDays}d / ${totalDays}d elapsed'),
                 SizedBox(height: 1),
@@ -1002,7 +1002,7 @@ class AppState extends State<CmdBridgeApp> {
                   Text('EXCEEDED', style: TextStyle(color: Colors.red, fontWeight: FontWeight.bold)),
               ]),
               SizedBox(height: 1),
-              Text('  Resets at: ${_fmtDate(c.fiveHour.resetTime)}',
+              Text('  Resets at: ${_fmtDate(c.fiveHour.resetTime)}  ${_relativeTime(c.fiveHour.resetTime)}',
                   style: TextStyle(color: Colors.grey)),
             ]),
           ));
@@ -1032,7 +1032,7 @@ class AppState extends State<CmdBridgeApp> {
                   Text('EXCEEDED', style: TextStyle(color: Colors.red, fontWeight: FontWeight.bold)),
               ]),
               SizedBox(height: 1),
-              Text('  Resets at: ${_fmtDate(c.weekly.resetTime)}',
+              Text('  Resets at: ${_fmtDate(c.weekly.resetTime)}  ${_relativeTime(c.weekly.resetTime)}',
                   style: TextStyle(color: Colors.grey)),
             ]),
           ));
@@ -1566,6 +1566,23 @@ class AppState extends State<CmdBridgeApp> {
     return '${dt.year}-${dt.month.toString().padLeft(2, '0')}-${dt.day.toString().padLeft(2, '0')} ${dt.hour.toString().padLeft(2, '0')}:${dt.minute.toString().padLeft(2, '0')}';
   }
 
+  String _relativeTime(DateTime target) {
+    final diff = target.difference(DateTime.now());
+    if (diff.isNegative) return '(overdue)';
+    if (diff.inDays >= 1) {
+      final hours = diff.inHours.remainder(24);
+      return '(in ${diff.inDays}d ${hours}h)';
+    }
+    if (diff.inHours >= 1) {
+      final mins = diff.inMinutes.remainder(60);
+      return '(in ${diff.inHours}h ${mins}m)';
+    }
+    if (diff.inMinutes >= 1) {
+      return '(in ${diff.inMinutes}m)';
+    }
+    return '(now)';
+  }
+
   String _fmtNum(int n) {
     if (n >= 1000000) return '${(n / 1000000).toStringAsFixed(2)}M';
     if (n >= 1000) return '${(n / 1000).toStringAsFixed(1)}K';