Fix: Progress-Timer zeigte negative Zahlen (-58:-10)

Ursache: Server sendete started_at als Lokalzeit (Europe/Berlin),
aber der Client interpretierte es als UTC via parseUTC().
Bei UTC+1 lag die Startzeit dadurch 1 Stunde in der Zukunft.

- orchestrator.py: started_at in WebSocket-Nachrichten als echtes UTC
  (ISO 8601 mit Z-Suffix) senden, DB-Timestamps bleiben Lokalzeit
- components.js: elapsed auf min. 0 clampen als Sicherheitsnetz

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

src/agents/orchestrator.py

@@ -548,6 +548,7 @@ class AgentOrchestrator:
 
             # Refresh-Log starten
             now = datetime.now(TIMEZONE).strftime('%Y-%m-%d %H:%M:%S')
+            now_utc = datetime.utcnow().strftime('%Y-%m-%dT%H:%M:%SZ')
             cursor = await db.execute(
                 "INSERT INTO refresh_log (incident_id, started_at, status, trigger_type, retry_count, tenant_id) VALUES (?, ?, 'running', ?, ?, ?)",
                 (incident_id, now, trigger_type, retry_count, tenant_id),
@@ -562,7 +563,7 @@ class AgentOrchestrator:
                 await self._ws_manager.broadcast_for_incident({
                     "type": "status_update",
                     "incident_id": incident_id,
-                    "data": {"status": research_status, "detail": research_detail, "started_at": now},
+                    "data": {"status": research_status, "detail": research_detail, "started_at": now_utc},
                 }, visibility, created_by, tenant_id)
 
             # Schritt 1+2: RSS-Feeds und Claude-Recherche parallel ausführen
@@ -840,7 +841,7 @@ class AgentOrchestrator:
                     await self._ws_manager.broadcast_for_incident({
                         "type": "status_update",
                         "incident_id": incident_id,
-                        "data": {"status": "factchecking", "detail": "Prüft Fakten gegen unabhängige Quellen...", "started_at": now},
+                        "data": {"status": "factchecking", "detail": "Prüft Fakten gegen unabhängige Quellen...", "started_at": now_utc},
                     }, visibility, created_by, tenant_id)
 
                 # Schritt 4: Faktencheck