feat(chat): Define initial messages on ChatScript

[skarllot]

Pull Request

Details on the issue fix or feature implementation

• Define the initial messages on ChatScript
• Increment progress using functional style
• Move business rule for stop keyword creation to ChatThread
• Fix to handle empty chat workspace correctly

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

Attention: Patch coverage is 83.33333% with 8 lines in your changes missing coverage. Please review.

Project coverage is 56.53%. Comparing base (0618b9b) to head (3fe7082).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/FlowPair/Chats/Services/ChatService.cs	12.50%	7 Missing ⚠️
src/FlowPair/Chats/Models/ChatScript.cs	75.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #34   +/-   ##
=======================================
  Coverage   56.53%   56.53%           
=======================================
  Files          72       72           
  Lines        1562     1569    +7     
  Branches      117      118    +1     
=======================================
+ Hits          883      887    +4     
- Misses        662      666    +4     
+ Partials       17       16    -1     

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