feat(scripts): add Get-StandardTimestamp utility to CIHelpers module (#1126)

## Description

Added a `Get-StandardTimestamp` function to `CIHelpers.psm1` that
returns the current UTC time as an ISO 8601 string
(`2025-01-15T18:30:00.0000000Z`). Five different timestamp expressions
existed across linting and security scripts with no shared utility,
making cross-script log correlation unreliable. This function provides a
single, authoritative source for consistent, timezone-unambiguous
timestamps across all scripts.

## Related Issue(s)

Closes #993

## Type of Change

Select all that apply:

**Code & Documentation:**

* [ ] Bug fix (non-breaking change fixing an issue)
* [x] New feature (non-breaking change adding functionality)
* [ ] Breaking change (fix or feature causing existing functionality to
change)
* [ ] Documentation update

**Infrastructure & Configuration:**

* [ ] GitHub Actions workflow
* [ ] Linting configuration (markdown, PowerShell, etc.)
* [ ] Security configuration
* [ ] DevContainer configuration
* [ ] Dependency update

**Other:**

* [x] Script/automation (`.ps1`, `.sh`, `.py`)
* [ ] Other (please describe):


## Testing

All validation was performed:

* `npm run lint:ps` — Passed. All PowerShell files pass PSScriptAnalyzer
checks with no issues.
* `npm run test:ps` — Passed. 73/73 Pester tests pass, including all 4
new `Get-StandardTimestamp` tests:
  * `Returns a string`
  * `Returns a non-empty value`
  * `Matches ISO 8601 UTC format ending in Z`
  * `Returns monotonically increasing timestamps on consecutive calls`
* Security analysis: No sensitive data, new dependencies, or privilege
scope changes detected.
* No manual testing required for this change; the function has no
external side effects or I/O.

## Checklist

### Required Checks

* [x] Documentation is updated (if applicable)
* [x] Files follow existing naming conventions
* [x] Changes are backwards compatible (if applicable)
* [x] Tests added for new functionality (if applicable)

### Required Automated Checks

The following validation commands must pass before merging:

* [x] Markdown linting: `npm run lint:md`
* [x] Spell checking: `npm run spell-check`
* [x] Frontmatter validation: `npm run lint:frontmatter`
* [x] Skill structure validation: `npm run validate:skills`
* [x] Link validation: `npm run lint:md-links`
* [x] PowerShell analysis: `npm run lint:ps`
* [x] Plugin freshness: `npm run plugin:generate`

## Security Considerations

<!-- ⚠️ WARNING: Do not commit sensitive information such as API keys,
passwords, or personal data -->
* [x] This PR does not contain any sensitive or NDA information
* [x] Any new dependencies have been reviewed for security issues (N/A —
no new dependencies)
* [x] Security-related scripts follow the principle of least privilege
(N/A — no security script changes)

## Additional Notes

This function is a prerequisite for issue #1000 (`Standardize timestamp
in SecurityHelpers.psm1 to use Get-StandardTimestamp`), which will be
addressed in a follow-up PR.

---------

Co-authored-by: Bill Berry <wberry@microsoft.com>
Co-authored-by: Bill Berry <WilliamBerryiii@users.noreply.github.com>

Author: AhmedMustafa249

scripts/lib/Modules/CIHelpers.psm1

@@ -550,7 +550,29 @@ function Publish-CIArtifact {
     }
 }
 
+function Get-StandardTimestamp {
+    <#
+    .SYNOPSIS
+    Returns the current UTC time as an ISO 8601 string.
+
+    .DESCRIPTION
+    Returns the current UTC time formatted with the round-trip specifier ("o"),
+    producing a string such as "2025-01-15T18:30:00.0000000Z". Use this
+    function wherever a timestamp is needed to ensure consistent, timezone-
+    unambiguous log output across all scripts.
+
+    .OUTPUTS
+    System.String - UTC timestamp in ISO 8601 round-trip format ending in Z.
+    #>
+    [CmdletBinding()]
+    [OutputType([string])]
+    param()
+
+    return (Get-Date).ToUniversalTime().ToString('o')
+}
+
 Export-ModuleMember -Function @(
+    'Get-StandardTimestamp',
     'ConvertTo-GitHubActionsEscaped',
     'ConvertTo-AzureDevOpsEscaped',
     'Get-CIPlatform',

scripts/tests/lib/CIHelpers.Tests.ps1

@@ -15,6 +15,33 @@ BeforeAll {
     Import-Module $mockPath -Force
 }
 
+Describe 'Get-StandardTimestamp' -Tag 'Unit' {
+    It 'Returns a string' {
+        Get-StandardTimestamp | Should -BeOfType [string]
+    }
+
+    It 'Returns a non-empty value' {
+        Get-StandardTimestamp | Should -Not -BeNullOrEmpty
+    }
+
+    It 'Matches ISO 8601 UTC format ending in Z' {
+        Get-StandardTimestamp | Should -Match '^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}\.\d+Z$'
+    }
+
+    It 'Returns monotonically increasing timestamps on consecutive calls' {
+        $earlier = [datetime]::new(2025, 1, 15, 18, 30, 0, [System.DateTimeKind]::Utc)
+        $later = $earlier.AddSeconds(1)
+
+        Mock Get-Date { $earlier } -ModuleName CIHelpers
+        $first = [datetime]::Parse((Get-StandardTimestamp))
+
+        Mock Get-Date { $later } -ModuleName CIHelpers
+        $second = [datetime]::Parse((Get-StandardTimestamp))
+
+        $second | Should -BeGreaterThan $first
+    }
+}
+
 Describe 'Get-CIPlatform' -Tag 'Unit' {
     BeforeAll {
         Save-CIEnvironment