feat: auto-email sending via SMTP (--send flag)

Closes #45

- New redmine_reporter/mailer.py: SMTP email sending with
  {author}/{period} template substitution, MIME attachment
  with correct content-type per file extension
- Config.get_email_config(): returns EmailConfig from YAML
  or None when not configured
- CLI --send flag: sends report after generation, works with
  --output, --commit, or standalone (saves to template path)
- 31 new tests (22 mailer + 6 CLI + 3 config)
- 249/249 tests passing, ruff clean, mypy clean

redmine_reporter/mailer.py

@@ -0,0 +1,120 @@
+"""Отправка сгенерированного отчёта по email через SMTP."""
+
+import email.charset as _charset
+import os
+import smtplib
+from email.mime.application import MIMEApplication
+from email.mime.multipart import MIMEMultipart
+from email.mime.text import MIMEText
+from typing import Dict
+
+from .client import RedmineAPIError
+from .config import EmailConfig
+
+# Use 8bit transfer encoding for UTF-8 so non-ASCII text (e.g. Russian)
+# appears literally in MIME output instead of base64.
+_charset.add_charset("utf-8", _charset.SHORTEST, None, "utf-8")
+
+SMTP_TIMEOUT = 30
+
+MIME_TYPES: Dict[str, str] = {
+    ".xlsx": "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet",
+    ".odt": "application/vnd.oasis.opendocument.text",
+    ".csv": "text/csv",
+    ".html": "text/html",
+    ".json": "application/json",
+    ".md": "text/markdown",
+}
+
+
+def _resolve_mime_type(file_path: str) -> str:
+    """Определяет MIME-тип по расширению файла."""
+    ext = os.path.splitext(file_path)[1].lower()
+    return MIME_TYPES.get(ext, "application/octet-stream")
+
+
+def build_message(
+    email_config: EmailConfig,
+    file_path: str,
+    author: str,
+    period: str,
+) -> MIMEMultipart:
+    """Формирует MIME-письмо с подстановками и вложением."""
+    subject = email_config.subject.replace("{author}", author).replace("{period}", period)
+    body = email_config.body_text.replace("{author}", author).replace("{period}", period)
+
+    msg = MIMEMultipart()
+    msg["Subject"] = subject
+    msg["From"] = email_config.from_
+    msg["To"] = ", ".join(email_config.to)
+    if email_config.cc:
+        msg["Cc"] = ", ".join(email_config.cc)
+
+    msg.attach(MIMEText(body, "plain", "utf-8"))
+
+    if email_config.attach:
+        try:
+            with open(file_path, "rb") as fh:
+                attachment = MIMEApplication(fh.read())
+        except OSError:
+            raise RedmineAPIError(
+                f"Не удалось прочитать файл отчёта: {file_path}"
+            ) from None
+        attachment.add_header(
+            "Content-Disposition",
+            "attachment",
+            filename=os.path.basename(file_path),
+        )
+        mime_type = _resolve_mime_type(file_path)
+        attachment.set_type(mime_type)
+        msg.attach(attachment)
+
+    return msg
+
+
+def send_report(
+    email_config: EmailConfig,
+    file_path: str,
+    author: str,
+    period: str,
+) -> None:
+    """Отправляет сгенерированный отчёт по email через SMTP.
+
+    Args:
+        email_config: Настройки SMTP и письма.
+        file_path: Путь к файлу отчёта для вложения.
+        author: Имя автора (для подстановки в тему/тело).
+        period: Строка периода (для подстановки в тему/тело).
+
+    Raises:
+        RedmineAPIError: При любой ошибке соединения или отправки.
+    """
+    smtp_cfg = email_config.smtp
+    msg = build_message(email_config, file_path, author, period)
+    all_recipients = list(email_config.to) + list(email_config.cc) + list(email_config.bcc)
+
+    try:
+        with smtplib.SMTP(smtp_cfg.host, smtp_cfg.port, timeout=SMTP_TIMEOUT) as server:
+            if smtp_cfg.tls:
+                server.starttls()
+            if smtp_cfg.user:
+                server.login(smtp_cfg.user, smtp_cfg.password)
+
+            server.send_message(msg, from_addr=email_config.from_, to_addrs=all_recipients)
+    except smtplib.SMTPAuthenticationError:
+        raise RedmineAPIError(
+            "Ошибка аутентификации SMTP. Проверьте логин и пароль."
+        ) from None
+    except TimeoutError:
+        raise RedmineAPIError(
+            "Таймаут соединения с SMTP-сервером."
+        ) from None
+    except smtplib.SMTPException as exc:
+        raise RedmineAPIError(
+            f"Ошибка отправки письма: {exc}"
+        ) from exc
+    except OSError as exc:
+        raise RedmineAPIError(
+            f"Не удалось подключиться к SMTP-серверу {smtp_cfg.host}:{smtp_cfg.port}"
+        ) from exc
+