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

redmine_reporter/formatters/csv.py

@@ -27,6 +27,7 @@ class CSVFormatter(Formatter):
             headers.append("Spent Time")
         writer.writerow(headers)
         for r in rows:
+            time_text = r["time_text"].replace("\n", " / ")
             data = [
                 r["project"],
                 r["version"],
@@ -35,7 +36,7 @@ class CSVFormatter(Formatter):
                 r["status_ru"],
             ]
             if not self.no_time:
-                data.append(r["time_text"])
+                data.append(time_text)
             writer.writerow(data)
         return output.getvalue()