feat(agent): Create repository context services

[skarllot]

Pull Request

The issue or feature being addressed

• Missing message to provide project key files content
• Missing message to provide repository structure

Details on the issue fix or feature implementation

• Update FxKit to 0.8.4 (support TryAggregate)
• Create DirectoryStructureMessageFactory to build a message with repository structure
• Create ProjectFilesMessageFactory to build a message with the content of project key files
• Fix ReadAllText(To) extension methods for using abstractions

Confirm the following

• I started this PR by branching from the head of the default branch
• I have targeted the PR to merge into the default branch
• I have included unit tests for the issue/feature
• I have successfully run a local build

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 46.75%. Comparing base (13f575e) to head (66ff812).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #26      +/-   ##
==========================================
+ Coverage   39.37%   46.75%   +7.38%     
==========================================
  Files          58       62       +4     
  Lines        1082     1172      +90     
  Branches       91       94       +3     
==========================================
+ Hits          426      548     +122     
+ Misses        643      612      -31     
+ Partials       13       12       -1     

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