style: enforce quoted literals, named parameters, and parameter validation

[tablackburn]

Background

instructions/powershell.instructions.md mandates three rules for in-tree code:

• Literal string parameter values are single-quoted (e.g., -Method 'Post', not -Method Post)
• Cmdlet calls use named parameters (when more than one argument is passed) (e.g., Split-Path -Path $p -Parent, not Split-Path -Parent $p)
• Every function parameter has an appropriate validator ([ValidateNotNullOrEmpty()], [ValidateRange], [ValidateSet], etc.)

These rules were applied to tablackburn/JsmOperations (PR #2) and the upstream tablackburn/PowerShellModuleTemplate (PR #23). This repo's first-party code hasn't been swept yet.

The recent line-ending normalization (PR #34) didn't touch the style rules above.

Scope

Apply the rules to:

• build.ps1
• Module source (ScheduledTasksManager/Public/*.ps1, ScheduledTasksManager/Private/*.ps1, ScheduledTasksManager/ScheduledTasksManager.psm1)
• First-party test files (the ones written for this module — tests/*.Tests.ps1)

Out of scope

Template-derived files come from tablackburn/PowerShellModuleTemplate and are tracked separately:

• tests/Help.tests.ps1
• tests/Manifest.tests.ps1
• tests/Meta.tests.ps1
• tests/MetaFixers.psm1
• tests/ManifestHelpers.psm1

tests/Integration/Start-IntegrationLab.ps1 is integration-test scaffolding — review separately.

Reference

tablackburn/JsmOperations#2 shows the canonical shape of these changes applied to a real module. The commits stacked on feature/v0.1.0-mvp walk through it (style sweep → naming refactor → expand-shorthand passes).

Acceptance criteria

• All in-scope style violations resolved
• ./build.ps1 still passes (PSScriptAnalyzer + Pester clean, coverage threshold preserved)
• Single-arg Write-Verbose / Write-Output / etc. stay positional (the rule is "named unless only one parameter")