enh: include cross-namespace IPM packages in contexts list

[isc-pbarton]

Resolves #952

Manual testing:

• docker compose up --build
• Create a second namespace in the container
• Set SourceControl.Git.Extension as source control extension for both namespaces
• git clone TestCoverage repo twice into separate directories in the container
• zpm "load -dev" each repo into a separate namespace
• Viewed Git Web UI, confirmed change context menu has options for USER:TESTCOVERAGE.ZPM and PBARTON:TESTCOVERAGE.ZPM
• Make a change in one of the repos. Switch back and forth between the two contexts in web ui and confirmed the workspace view updated.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 49.11%. Comparing base (578aaf7) to head (c684c05).

Files with missing lines	Patch %	Lines
cls/SourceControl/Git/Utils.cls	0.00%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #953      +/-   ##
==========================================
- Coverage   49.18%   49.11%   -0.08%     
==========================================
  Files          23       23              
  Lines        3269     3274       +5     
==========================================
  Hits         1608     1608              
- Misses       1661     1666       +5     

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