feat: JSON, Excel export and time summary

- #23: add JSONFormatter and XLSXFormatter
- add openpyxl dependency for .xlsx export
- #22: add --summary flag and calculate_summary() in report_builder
- ReportRow now carries raw hours for summary calculations
- update CLI help and README with .json/.xlsx formats and --summary
- add tests for new formatters and summary computation

Closes #22, closes #23

redmine_reporter/formatters/json.py

@@ -0,0 +1,31 @@
+import json
+from typing import List
+
+from ..types import ReportRow
+from .base import Formatter
+
+
+class JSONFormatter(Formatter):
+    """Форматтер для экспорта отчёта в JSON."""
+
+    def __init__(self, **_kwargs):
+        super().__init__()
+
+    def format(self, rows: List[ReportRow]) -> str:
+        data = [
+            {
+                "project": r["project"],
+                "version": r["version"],
+                "issue_id": r["issue_id"],
+                "subject": r["subject"],
+                "status": r["status_ru"],
+                "time": r["time_text"],
+            }
+            for r in rows
+        ]
+        return json.dumps(data, ensure_ascii=False, indent=2)
+
+    def save(self, rows: List[ReportRow], output_path: str) -> None:
+        content = self.format(rows)
+        with open(output_path, "w", encoding="utf-8") as f:
+            f.write(content)