fix(time): Mikrosekunden bei Zeitstempeln kappen

start_time/end_time/break_start wurden mit vollen Mikrosekunden gespeichert
(datetime.now(timezone.utc).time() ohne microsecond=0), was Clients ohne
Mikrosekunden-Parsing brechen konnte (siehe Mobile-App-Crash). Sekunden-
Genauigkeit reicht für Zeiterfassung.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Dzdm3EWeNdYFUuXFRJryA1

backend/app/services/time_service.py

@@ -79,7 +79,7 @@ class TimeService:
         db: AsyncSession,
     ) -> tuple[TimeEntry, list[str]]:
         today = datetime.now(timezone.utc).date()
-        now_time = datetime.now(timezone.utc).time().replace(tzinfo=None)
+        now_time = datetime.now(timezone.utc).time().replace(microsecond=0, tzinfo=None)
 
         # Offenen Eintrag für heute prüfen
         open_entry = await self._get_open_entry(user.id, db)
@@ -125,7 +125,7 @@ class TimeService:
         if entry is None:
             raise HTTPException(status_code=404, detail="Kein offener Zeitstempel gefunden.")
 
-        now_time = datetime.now(timezone.utc).time().replace(tzinfo=None)
+        now_time = datetime.now(timezone.utc).time().replace(microsecond=0, tzinfo=None)
 
         # Aktive Pause beenden falls vergessen
         if entry.break_start is not None:
@@ -148,7 +148,7 @@ class TimeService:
         if entry.break_start is not None:
             raise HTTPException(status_code=409, detail="Pause bereits aktiv.")
 
-        now_time = datetime.now(timezone.utc).time().replace(tzinfo=None)
+        now_time = datetime.now(timezone.utc).time().replace(microsecond=0, tzinfo=None)
         entry.break_start = now_time
         entry.updated_at = datetime.now(timezone.utc)
         return entry
@@ -160,7 +160,7 @@ class TimeService:
         if entry.break_start is None:
             raise HTTPException(status_code=409, detail="Keine aktive Pause.")
 
-        now_time = datetime.now(timezone.utc).time().replace(tzinfo=None)
+        now_time = datetime.now(timezone.utc).time().replace(microsecond=0, tzinfo=None)
         extra = self._calc_break_minutes(entry.break_start, now_time)
         entry.break_minutes += extra
         entry.break_start = None