docs: update README, CONFIG and pyproject.toml for --send feature

- README: add --send flag to features, usage examples, full flag list;
  replace black/isort with ruff in dev section; add email config
  template variables docs
- CONFIG: new email section with all fields documented, --send usage
  examples, error handling and flag compatibility table
- pyproject.toml: remove unused black and isort from dev dependencies
  and their tool configs (project uses ruff for both lint and format)

pyproject.toml

@@ -30,8 +30,6 @@ dependencies = [
 [project.optional-dependencies]
 dev = [
     "pytest>=7.0",
-    "black>=23.0",
-    "isort>=5.12",
     "mypy>=1.0",
     "ruff>=0.1.0",
 ]
@@ -46,14 +44,6 @@ include = ["redmine_reporter*"]
 [tool.setuptools.package-data]
 "redmine_reporter" = ["templates/template.odt"]
 
-[tool.black]
-line-length = 100
-target-version = ['py39']
-
-[tool.isort]
-profile = "black"
-multi_line_output = 3
-
 [tool.mypy]
 warn_unused_configs = true