feat: add HTML email body for --send (#48)

Add email.html config flag (default false). When enabled, --send
includes an HTML version of the report body generated via HTMLFormatter
alongside the plain-text part in a multipart/alternative message.

- EmailConfig gains html: bool field
- mailer.build_message/send_report accept rows for HTML generation
- CLI passes rows to send_report
- --init-config generates email.html: false
- README.md and docs/CONFIG.md updated

Bump version to 1.10.0.

Closes #48

tests/test_config.py

@@ -5,7 +5,12 @@ from unittest import mock
 
 import pytest
 
-from redmine_reporter.config import DEFAULT_REDMINE_VERIFY, AppConfig, Config
+from redmine_reporter.config import (
+    DEFAULT_REDMINE_VERIFY,
+    AppConfig,
+    Config,
+    EmailConfig,
+)
 
 
 @mock.patch.dict(
@@ -613,6 +618,54 @@ class TestGetEmailConfig:
             assert Config.get_email_config() is None
 
 
+class TestEmailConfigHtml:
+    """Tests for EmailConfig.html field."""
+
+    def test_email_config_html_from_yaml(self):
+        """email.html: true загружается из YAML."""
+        with tempfile.TemporaryDirectory() as tmp:
+            yaml_path = Path(tmp) / "config.yml"
+            yaml_path.write_text(
+                "email:\n  html: true\n  smtp:\n    host: smtp.example.com\n"
+            )
+
+            cfg = AppConfig.from_yaml(yaml_path)
+            assert cfg.email.html is True
+
+    def test_email_config_html_defaults_to_false(self):
+        """email.html по умолчанию False."""
+        assert EmailConfig().html is False
+
+        with tempfile.TemporaryDirectory() as tmp:
+            yaml_path = Path(tmp) / "config.yml"
+            yaml_path.write_text("email:\n  smtp:\n    host: smtp.example.com\n")
+
+            cfg = AppConfig.from_yaml(yaml_path)
+            assert cfg.email.html is False
+
+    def test_email_config_html_false_from_yaml(self):
+        """email.html: false явно загружается из YAML."""
+        with tempfile.TemporaryDirectory() as tmp:
+            yaml_path = Path(tmp) / "config.yml"
+            yaml_path.write_text(
+                "email:\n  html: false\n  smtp:\n    host: smtp.example.com\n"
+            )
+
+            cfg = AppConfig.from_yaml(yaml_path)
+            assert cfg.email.html is False
+
+    def test_email_config_html_invalid_string_defaults_to_false(self):
+        """email.html со строкой 'invalid' приводится к False."""
+        with tempfile.TemporaryDirectory() as tmp:
+            yaml_path = Path(tmp) / "config.yml"
+            yaml_path.write_text(
+                "email:\n  html: 'invalid'\n  smtp:\n    host: smtp.example.com\n"
+            )
+
+            cfg = AppConfig.from_yaml(yaml_path)
+            assert cfg.email.html is False
+
+
 class TestReportNoTime:
     """Tests for Config.get_report_no_time()."""