fix: normalize datetimes to aware UTC in dedup

Dedup with precision=datetime crashed with TypeError: redminelib returns
naive created_on/updated_on while the cutoff from _compute_dedup_cutoff
is aware UTC. Normalize at a single point: _parse_datetime now always
returns an aware datetime (naive treated as UTC), matching its docstring.
The dedup cutoff is normalized the same way, and any residual comparison
TypeError is wrapped in RedmineAPIError instead of leaking raw.

Also fix --commit saving last_used.to as naive local time; it now stores
aware UTC (datetime.now(timezone.utc)) so the next run computes a correct
aware cutoff.

Closes #58

redmine_reporter/client.py

@@ -1,4 +1,4 @@
-from datetime import datetime
+from datetime import datetime, timezone
 from typing import Any, Dict, List, Optional, Tuple, Union
 
 import requests
@@ -150,20 +150,28 @@ def _parse_datetime(value: Any) -> Optional[datetime]:
 
     Accepts datetime objects, ISO strings (with or without timezone),
     or None. Returns a timezone-aware datetime or None.
+    Naive datetimes are treated as UTC (#58).
     """
     if value is None:
         return None
     if isinstance(value, datetime):
-        return value
+        return _ensure_aware_utc(value)
     if isinstance(value, str):
         try:
             dt = datetime.fromisoformat(value.replace("Z", "+00:00"))
-            return dt
+            return _ensure_aware_utc(dt)
         except (ValueError, TypeError):
             return None
     return None
 
 
+def _ensure_aware_utc(dt: datetime) -> datetime:
+    """Возвращает aware datetime; naive трактуется как UTC (#58)."""
+    if dt.tzinfo is None:
+        return dt.replace(tzinfo=timezone.utc)
+    return dt
+
+
 def _fetch_issues_chunked(redmine: Redmine, issue_ids: List[int]) -> List[Issue]:
     """Загружает задачи чанками, чтобы не превышать лимит длины URL (#21)."""
     all_issues: List[Issue] = []
@@ -277,20 +285,29 @@ def fetch_issues_with_spent_time(
     # Запись исключается, если BOTH created_on AND updated_on < dedup_before.
     # Записи без метаданных (created_on/updated_on == None) не фильтруются.
     if dedup_before is not None:
+        # Нормализуем cutoff к aware UTC (#58): naive cutoff трактуем как UTC,
+        # чтобы сравнение с нормализованными created_on/updated_on было корректным.
+        dedup_before = _ensure_aware_utc(dedup_before)
         filtered: list = []
-        for entry in time_entries:
-            created = _parse_datetime(getattr(entry, "created_on", None))
-            updated = _parse_datetime(getattr(entry, "updated_on", None))
+        try:
+            for entry in time_entries:
+                created = _parse_datetime(getattr(entry, "created_on", None))
+                updated = _parse_datetime(getattr(entry, "updated_on", None))
 
-            if created is None and updated is None:
-                filtered.append(entry)
-            elif created is not None and updated is not None:
-                if created >= dedup_before and updated >= dedup_before:
+                if created is None and updated is None:
                     filtered.append(entry)
-            elif created is not None and created >= dedup_before:
-                filtered.append(entry)
-            elif updated is not None and updated >= dedup_before:
-                filtered.append(entry)
+                elif created is not None and updated is not None:
+                    if created >= dedup_before and updated >= dedup_before:
+                        filtered.append(entry)
+                elif created is not None and created >= dedup_before:
+                    filtered.append(entry)
+                elif updated is not None and updated >= dedup_before:
+                    filtered.append(entry)
+        except TypeError as exc:
+            raise RedmineAPIError(
+                f"Failed to compare time entry dates with deduplication cutoff: {exc}",
+                original=exc,
+            ) from exc
         time_entries = filtered
 
     # Агрегируем часы по issue.id (и активности, если требуется)