Fix 9 bugs: ODT covered-cells, CSV BOM, HTML charset, stderr, dead code

- #13 (critical): Add CoveredTableCell elements to ODT for valid row spans (ODF 1.2)
- #28: Move "Total issues" info message from stdout to stderr (clean pipe output)
- #27: Wrap HTML export in full document with DOCTYPE and meta charset utf-8
- #26: Save CSV with utf-8-sig encoding (UTF-8 BOM for Excel compatibility)
- #31: Document CSV uses full project/version values (not display_* like console/MD)
- #30: Fix ODT header formatting when author is empty (no leading dot/space)
- #36: Remove test_cli_smoke_empty testing unreachable code path (return [])
- #37: Remove unused mock_path variable in ODT test fixture
- #34: Remove unreachable len(parts) != 2 check in parse_date_range

Closes #13, #28, #27, #26, #31, #30, #36, #37, #34

redmine_reporter/cli.py

@@ -15,8 +15,6 @@ def parse_date_range(date_arg: str) -> tuple[str, str]:
     if "--" not in date_arg:
         raise ValueError("Date range must be in format YYYY-MM-DD--YYYY-MM-DD")
     parts = date_arg.split("--", 1)
-    if len(parts) != 2:
-        raise ValueError("Invalid date range format")
 
     from_date, to_date = parts[0].strip(), parts[1].strip()
     date_pattern = r"\d{4}-\d{2}-\d{2}"
@@ -85,7 +83,7 @@ def main(argv: Optional[List[str]] = None) -> int:
         print("ℹ️  No time entries found in the given period.", file=sys.stderr)
         return 0
 
-    print(f"✅ Total issues: {len(issue_hours)} [{args.date}]")
+    print(f"✅ Total issues: {len(issue_hours)} [{args.date}]", file=sys.stderr)
 
     rows = build_grouped_report(issue_hours, fill_time=not args.no_time)