Document the PowerShell output streams and prefer implicit output over return

[MariusStorhaug]

Context

index.md says "emit objects, not formatted text" and reserves Write-Host for genuine console UX, with Write-Verbose / Write-Information for narration. Functions.md covers throw vs Write-Error.

Gap

We do not give the full output-stream taxonomy, nor the "don't use return to emit" idiom:

• Implicit output for results — prefer placing the object on its own line over return $obj; in a pipeline function, emit from the process block, not end.
• Write-Verbose for status and why-a-path-was-chosen (useful, not necessary).
• Write-Progress for progress (ephemeral — never the only place information the user needs appears).
• Write-Debug for maintainer breadcrumbs.
• Write-Warning and Write-Error for warnings and non-terminating errors.
• Write-Host only for Show- / Format- verbs or interactive prompts.
• [CmdletBinding()] is what enables the -Verbose / -Debug switches that turn those streams on.

Proposed change

Add an "Output streams" subsection to Functions.md (or the index.md idioms) with a stream-per-purpose list, and add "prefer implicit output over return" to the Functions output rules.

Source

PoshCode — Best Practices "Output and Formatting"; Style Guide "Function Structure".

Acceptance

The standard lists each output stream with its purpose, restricts Write-Host, and states the implicit-output-over-return rule.