feat: centralize PowerShell dependency updates

[lipkau]

Summary

• run scheduled and manual PowerShell dependency updates from the organization .github repository
• select repositories centrally and authenticate with short-lived GitHub App tokens
• delegate dependency resolution to AtlassianPS.Standards 0.3.1 and synchronize immutable workflow references
• create or refresh one dependency pull request per target repository
• validate the controller with Pester, PSScriptAnalyzer, and workflow linting

Configuration required

Create an organization GitHub App with write access to contents, issues, pull requests, and workflows for the configured target repositories. Add its credentials as DEPENDENCY_UPDATE_APP_ID and DEPENDENCY_UPDATE_APP_PRIVATE_KEY secrets.

Validation

• actionlint: passed
• PSScriptAnalyzer 1.25.0: passed
• controller Pester tests: 6 passed
• end-to-end disposable repository update: passed
• independent review: no remaining Critical or Important findings

Related pull requests

• AtlassianPS.Configuration #43
• ConfluencePS #262
• JiraAgilePS #47
• JiraPS #709