fix: UTC timezone suffix missing from all isoformat() timestamp outputs

db.py returned all datetime columns (first_seen, last_seen, resolved_at,
created_at, expires_at) as bare ISO strings like "2026-03-14T14:14:21"
with no timezone marker. Per the ECMAScript spec, new Date() on a
datetime string without timezone treats it as LOCAL time, not UTC.
This made lt.time.ago() and stale-detection wrong for any user whose
browser is not in UTC — event ages and stale warnings would be off by
the client's UTC offset.

monitor.py had the same issue on the network_snapshot 'updated' field.

Fix: append 'Z' to all isoformat() calls (UTC datetimes confirmed by
MySQL server timezone and _now_utc() pattern used throughout codebase).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

db.py

@@ -182,7 +182,7 @@ def get_active_events(limit: int = 200, offset: int = 0) -> list:
             for r in rows:
                 for k in ('first_seen', 'last_seen'):
                     if r.get(k) and hasattr(r[k], 'isoformat'):
-                        r[k] = r[k].isoformat()
+                        r[k] = r[k].isoformat() + 'Z'
             return rows
 
 
@@ -210,7 +210,7 @@ def get_recent_resolved(hours: int = 24, limit: int = 50) -> list:
             for r in rows:
                 for k in ('first_seen', 'last_seen', 'resolved_at'):
                     if r.get(k) and hasattr(r[k], 'isoformat'):
-                        r[k] = r[k].isoformat()
+                        r[k] = r[k].isoformat() + 'Z'
             return rows
 
 
@@ -252,7 +252,7 @@ def get_active_suppressions() -> list:
             for r in rows:
                 for k in ('created_at', 'expires_at'):
                     if r.get(k) and hasattr(r[k], 'isoformat'):
-                        r[k] = r[k].isoformat()
+                        r[k] = r[k].isoformat() + 'Z'
             return rows
 
 
@@ -267,7 +267,7 @@ def get_suppression_history(limit: int = 50) -> list:
             for r in rows:
                 for k in ('created_at', 'expires_at'):
                     if r.get(k) and hasattr(r[k], 'isoformat'):
-                        r[k] = r[k].isoformat()
+                        r[k] = r[k].isoformat() + 'Z'
             return rows
 
 

monitor.py

@@ -918,7 +918,7 @@ class NetworkMonitor:
         return {
             'hosts': hosts,
             'unifi': display_unifi,
-            'updated': datetime.utcnow().isoformat(),
+            'updated': datetime.utcnow().isoformat() + 'Z',
         }
 
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