enhancement: Add cleanup scripts for remaining discovered resource types

[Daren9m]

Description

Discovery finds resource types that have no corresponding cleanup scripts:

• Empty App Service Plans (5 found) — no Remove-EmptyAppServicePlans.ps1
• Orphaned NICs (8 found) — no Remove-OrphanedNICs.ps1
• Empty Load Balancers (2 found) — no Remove-EmptyLoadBalancers.ps1
• Orphaned Route Tables (0 found, but query exists) — no cleanup script
• Idle SQL databases (13 found via metrics) — no cleanup script

Acceptance Criteria

• Remove-EmptyAppServicePlans.ps1 with -WhatIf, lock check, tag exclusions
• Remove-OrphanedNICs.ps1 with PE-managed NIC detection
• Remove-EmptyLoadBalancers.ps1 with SKU-aware priority
• Pester tests for each new script
• Update Invoke-CleanupDryRun.ps1 and Invoke-CleanupExecution.ps1 script registries