feat(cli): configurable --target-coverage CE lookback window (closes #360)

[cristim]

Summary

• existingCoverageLookbackDays was hardcoded to 30 in cmd/multi_service.go. Operators reconciling CUDly's ExistingCoverage column against the AWS console coverage-report export could not align the windows, causing percentage discrepancies for the same pool (see issue description for a concrete RDS example).
• Adds --coverage-lookback-days flag (default 30, matching CE's UI default) that sets Config.CoverageLookbackDays and is threaded into GetRICoverageMap via fetchExistingCoverage.
• Validation in validateNumericRanges rejects values < 1 with a clear error message.

Design choices

Decision	Choice	Rationale
Flag name	--coverage-lookback-days	Matches the *-days suffix convention used by --rebuy-window-days in the same CLI
Default value	30	Matches CE's UI default and the previous hardcoded constant; no behaviour change on upgrade
Env-var?	Not added	Other flags in this CLI don't expose env-var aliases; consistent with existing convention
Validation lower bound	>= 1	CE requires start < end; a 0-day window is undefined

Files changed

• cmd/main.go - Config.CoverageLookbackDays field + flag registration in init()
• cmd/validators.go - validateNumericRanges guard (< 1 rejected)
• cmd/multi_service.go - drop existingCoverageLookbackDays constant; thread cfg.CoverageLookbackDays (with <= 0 -> 30 fallback) into adapter.GetRICoverageMap
• cmd/validators_test.go - TestValidateCoverageLookbackDays (5 cases); existing tests updated to set CoverageLookbackDays: 30
• cmd/multi_service_coverage_test.go - TestFetchExistingCoverage_LookbackDays (3 cases)

Test counts

1031 passed, 0 failed (up from 1019 passed, 12 failed before fixing test setup)

Note for operators

To reconcile CUDly's ExistingCoverage column against the AWS console reservations-coverage report, pass --coverage-lookback-days matching the report's date range (e.g. --coverage-lookback-days 30 for a 30-day window, --coverage-lookback-days 14 for a 2-week export). The API has no anchor-alignment option so an exact day match is the best available reconciliation.

Closes #360

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⚙️ Run configuration

Configuration used: defaults

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Run ID: 424bd9cb-e18d-4167-ab5b-97d112596191

📥 Commits

Reviewing files that changed from the base of the PR and between 4956d66 and bfc29ef.

📒 Files selected for processing (5)

• cmd/main.go
• cmd/multi_service.go
• cmd/multi_service_coverage_test.go
• cmd/validators.go
• cmd/validators_test.go

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