Allow deletion of legacy suspended organizations

[niemyjski]

What changed

Migrate the exact legacy Stripe suspension marker before normal organization writes validate it.

Evidence

• Git history shows the old Stripe event handler wrote the literal "Stripe" into SuspendedByUserId in both suspension paths.
• A later Stripe billing change introduced the all-zero 24-character system user ID used today.
• Existing SystemUserId constants for OAuth and predefined saved views are different IDs, so they are not interchangeable.

Fix

• Centralize the Stripe-specific legacy and current IDs.
• Add version 7 as a versioned, resumable migration.
• Scan suspended organizations, including soft-deleted records, through the existing typed organization repository.
• Filter the unmapped legacy field from loaded source and replace only the exact legacy marker.
• Refresh the current organization index after writes so reruns and subsequent API requests observe the migration.
• Preserve suspension metadata so deleting and restoring an organization does not silently clear its suspension state.

Verification

• Five integration tests cover historical conversion, non-target records, soft-deleted records, idempotent reruns, and more than one migration page.
• Organization endpoint regression coverage verifies suspension state survives delete and restore.
• Migration registration test verifies version 7 and VersionedAndResumable registration.
• dotnet build Exceptionless.slnx --no-restore -m:1
• Hosted Build run 31840728876 passed all required checks.

No production identifiers or customer data are included.

[github-actions]

Package	Line Rate	Branch Rate	Complexity	Health
Exceptionless.Insulation	37%	35%	286	❌
Exceptionless.Core	75%	67%	10012	➖
Exceptionless.Web	85%	69%	7033	✔
Exceptionless.AppHost	38%	40%	139	❌
Summary	78% (23525 / 30333)	67% (11041 / 16544)	17470	✔