feat(xlsx): make Excel export production-grade

- Add merge cells for project/version groups.
- Add numeric Hours column and human-readable Spent Time.
- Add version/project/grand totals.
- Apply auto-width, freeze panes, auto-filter and styling.
- Respect --no-time: keep columns empty, skip totals.
- Pass no_time flag through formatter factory to all file formatters.
- Add tests for XLSX features and --no-time behavior.

Closes #38

.gitignore

@@ -88,7 +88,7 @@ secrets.json
 
 # Just in case
 .~*
-report.odt
-report.csv
-report.md
+# Local report outputs
+report.*
+rep.*
 *.html