feat(errors): provide readable Redmine API error messages

- Introduce RedmineAPIError with human-friendly messages.
- Distinguish AuthError, ForbiddenError, HTTP status codes, timeouts
  and connection errors in client.py.
- Update CLI to print the readable message instead of generic
  "Redmine API error: ...".
- Log original exception with traceback when --debug is enabled.
- Add tests for all error paths and CLI output.

Closes #39

redmine_reporter/client.py

@@ -2,6 +2,7 @@ from typing import Any, Dict, List, Optional, Tuple
 
 import requests
 from redminelib import Redmine
+from redminelib.exceptions import AuthError, ForbiddenError
 from redminelib.resources import Issue
 from urllib3.util.retry import Retry
 
@@ -14,6 +15,15 @@ REQUEST_TIMEOUT = 30
 ISSUE_ID_CHUNK_SIZE = 100
 
 
+class RedmineAPIError(Exception):
+    """Пользовательское исключение с понятным сообщением об ошибке Redmine API."""
+
+    def __init__(self, message: str, original: Optional[Exception] = None):
+        super().__init__(message)
+        self.message = message
+        self.original = original
+
+
 def _get_redmine_auth_kwargs() -> Dict[str, Any]:
     """Return Redmine auth kwargs. API key has priority over legacy password auth."""
     api_key = Config.get_redmine_api_key()
@@ -56,6 +66,49 @@ def _create_redmine() -> Redmine:
     return redmine
 
 
+def _format_redmine_error(exc: Exception) -> str:
+    """Преобразует исключение Redmine/requests в понятное сообщение."""
+    if isinstance(exc, AuthError):
+        return (
+            "Authentication failed: invalid API key, login or password. "
+            "Check REDMINE_API_KEY / REDMINE_USER / REDMINE_PASSWORD."
+        )
+    if isinstance(exc, ForbiddenError):
+        return (
+            "Access denied: your Redmine account does not have permission "
+            "to read time entries or issues."
+        )
+
+    # requests HTTPError может быть обёрнуто в python-redmine
+    original = getattr(exc, "response", None)
+    if original is None:
+        original = exc
+
+    response = getattr(original, "response", None)
+    if response is not None and hasattr(response, "status_code"):
+        status = response.status_code
+        if status == 401:
+            return "Authentication failed (HTTP 401): check your API key or login/password."
+        if status == 403:
+            return "Access denied (HTTP 403): insufficient Redmine permissions."
+        if status == 404:
+            return "Redmine endpoint not found (HTTP 404): check REDMINE_URL."
+        if status == 429:
+            return "Too many requests (HTTP 429): Redmine rate limit exceeded."
+        if 500 <= status < 600:
+            return f"Redmine server error (HTTP {status}): try again later."
+        return f"Redmine API returned HTTP {status}."
+
+    if isinstance(exc, requests.exceptions.Timeout):
+        return f"Redmine request timed out after {REQUEST_TIMEOUT} seconds."
+    if isinstance(exc, requests.exceptions.ConnectionError):
+        return "Cannot connect to Redmine: check the URL and network."
+    if isinstance(exc, requests.exceptions.RequestException):
+        return f"Network error while calling Redmine: {exc}"
+
+    return str(exc)
+
+
 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] = []
@@ -74,14 +127,17 @@ def fetch_issues_with_spent_time(
     Fetch unique issues linked to time entries of the current user in given date range,
     along with total spent hours per issue.
     Returns list of (issue, total_hours) tuples.
+    Raises RedmineAPIError on API/auth/network failures.
     """
 
-    redmine = _create_redmine()
-
-    current_user = redmine.user.get("current")
-    time_entries = redmine.time_entry.filter(
-        user_id=current_user.id, from_date=from_date, to_date=to_date
-    )
+    try:
+        redmine = _create_redmine()
+        current_user = redmine.user.get("current")
+        time_entries = redmine.time_entry.filter(
+            user_id=current_user.id, from_date=from_date, to_date=to_date
+        )
+    except Exception as exc:
+        raise RedmineAPIError(_format_redmine_error(exc), original=exc) from exc
 
     # Агрегируем часы по issue.id
     spent_time: Dict[int, float] = {}
@@ -96,8 +152,11 @@ def fetch_issues_with_spent_time(
         return None
 
     # Загружаем полные объекты задач чанками (#21)
-    sorted_ids = sorted(issue_ids)
-    issues = _fetch_issues_chunked(redmine, sorted_ids)
+    try:
+        sorted_ids = sorted(issue_ids)
+        issues = _fetch_issues_chunked(redmine, sorted_ids)
+    except Exception as exc:
+        raise RedmineAPIError(_format_redmine_error(exc), original=exc) from exc
 
     # Сопоставляем задачи с суммарным временем.
     # Сортировка выполняется в report_builder.build_grouped_report,