feat(activity): add --by-activity flag to break down spent time by activity type

- Load time entry activity names from Redmine enumeration.
- Aggregate hours per issue and per activity in fetch_issues_with_spent_time.
- Add --by-activity CLI flag and propagate it through report builder,
  summary, and all formatters (console, CSV, HTML, JSON, ODT).
- Keep backward-compatible 2-tuple input in build_grouped_report.
- Bump version to 1.8.0.

Closes #41

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "redmine-reporter"
-version = "1.7.0"
+version = "1.8.0"
 description = "Redmine time-entry based issue reporter for internal use"
 readme = "README.md"
 authors = [{ name = "Artem Kokos", email = "artem-kokos@mail.ru" }]