Cleanup and modernize codebase with PS7/C# latest features

[marcelloformica]

Summary

Cleanup, modernize, and document both PowerShell and C# codebases with latest language features and best practices.

Changes

PowerShell (get-availability.ps1)

• Added doc-comments to all helper functions and critical code sections
• Added descriptive section headers for batch config, endpoint validation, batch metrics, per-resource metrics, investigation, and output
• Replaced \if/else\ with PS7 ternary operators in multiple locations
• Fixed batch-implies semantics: use \System.Management.Automation.PSBoundParametersDictionary.ContainsKey('BatchSize')\ instead of \ -ne 10\
• Added classification precedence documentation to \Invoke-SuspectGapInvestigation\
• Added inline comments to investigation helpers

C# (.NET 10)

• Replaced \Math.Max/Min\ with \Math.Clamp\ in Program.cs
• Consolidated triple \TryGetValue\ dictionary lookups into a single block
• Changed \string[]\ to \ReadOnlySpan\ for timestamp formats (stack allocation) in ActivityLogService.cs
• Added <summary>\ doc-comments to helper methods across services
• Added BatchMetricsService.cs to source control

Documentation

• Updated README with batch mode parameters and usage examples for both C# and PowerShell
• Added batch API mode bullet to Architecture notes