Improve command discoverability: a selection matrix doc + `-Help` summary for the ScubaGear module

[DickTracyII]

Prerequisites

• This issue has an informative and human-readable title.
• Assignee should meet with issue author before starting work.

💡 Summary

ScubaGear now exports a growing set of user-facing commands (Invoke-SCuBA, Invoke-SCuBACached, Invoke-SCuBADiff, New-SCuBAConfig, Start-SCuBAConfigApp, Start-SCuBAConfigAnalyzer, Show-SCuBABaselinePolicyViewer, plus setup/dependency commands). New and returning users struggle to know which command to use, when, and why without reading several long docs. This issue adds two low-cost, high-value discoverability aids:

1. A tool-selection matrix page in docs/: a one-screen cheat sheet mapping each command to a BLUF, "use it when," and "why it matters."
2. A -Help summary surfaced from the module itself so users get the same at-a-glance guidance directly in the terminal, without leaving PowerShell.

Motivation and context

• The command surface keeps expanding; existing docs are thorough but require a lot of reading to answer "which one do I run?"
• Users often discover commands by accident or word-of-mouth, then reach for the wrong tool (e.g., re-scanning when Invoke-SCuBACached or Invoke-SCuBADiff would do).
• A concise decision aid - in docs and in-terminal - shortens time-to-first-success and reduces support questions.

Implementation notes

Docs (partially drafted)

• docs/misc/tool-selection-matrix.md with two matrices:
  • Configuration & analysis tools (New-SCuBAConfig, Start-SCuBAConfigApp, Start-SCuBAConfigAnalyzer, Show-SCuBABaselinePolicyViewer, Invoke-SCuBADiff).
  • Core assessment commands (Invoke-SCuBA, Invoke-SCuBACached, Disconnect-SCuBATenant, Install-ScubaDependencies, Install-OPAforSCuBA, Get-ScubaGearDependencyStatus, Update-ScubaGear).
  • Include a Mermaid flow showing how the tools chain together.
• Link the page from README.md (Configuration & Usage + Additional Resources).

In-terminal help

• Add a lightweight help summary command, e.g. Get-ScubaHelp (verb-approved) that prints the same matrix content as a formatted table grouped by category, with a one-line BLUF per command and a pointer to the docs page.
• Consider a -Help switch on Invoke-SCuBA that routes to the same summary, since Invoke-SCuBA is the most common entry point and where users land first.
• Source the summary from a single data structure (hashtable/JSON) so the docs matrix and the in-terminal output can be generated/validated from one source of truth and won't drift.
• Keep it dependency-free and offline; no Graph/tenant calls.
• Export the new command in ScubaGear.psd1 (FunctionsToExport) and add a comment-based help block.

Acceptance criteria

• docs/misc/tool-selection-matrix.md exists with both matrices (BLUF / when / why) and a Mermaid diagram.
• README.md links to the new matrix page in at least one discoverable location.
• A terminal help summary is available (Get-ScubaHelp and/or Invoke-SCuBA -Help) that lists each user-facing command with a one-line BLUF, grouped by category, and points to the docs page.
• The help command runs fully offline with no tenant/Graph calls and no errors on a clean install.
• The new command is exported in ScubaGear.psd1 and has comment-based help.
• In-terminal summary and docs matrix stay consistent (ideally generated/validated from a single source).
• Unit test(s) cover the help command output (e.g., every exported user-facing command appears in the summary).
• Docs and any new command follow the repo CONTENTSTYLEGUIDE.md and pass PSScriptAnalyzer.