fix(csv): explicit --coverage 80 is treated as unset on --input-csv runs and buys 100% #2236

Summary

On an --input-csv run, an explicit --coverage 80 is treated as "not set": the run skips sizing and buys 100% of each CSV row's count. This was split from #1613 (finding M1) and re-verified on origin/main fd0af9f.

Cause

• determineCSVCoverage (cmd/multi_service_csv.go:23-30) maps the flag's default value, 80.0, to 100.
• It is called at cmd/multi_service.go:746. When it returns 100, sizing is skipped (cmd/multi_service.go:931).
• Because the check compares against the default value, the code cannot tell an explicitly passed --coverage 80 from no flag at all.

Fix

Use cmd.Flags().Changed("coverage") to tell an explicit value from the default, as cmd/validators.go already does for other flags. Add a regression test showing that an explicit --coverage 80 scales a CSV row's count to 80% on a dry run.

Coordination

The fix touches cmd/multi_service_csv.go and cmd/multi_service.go, and the open #2203 touches both files. Land this after #2203, or rebase it onto #2203.