feat(code): embed guidelines in the code chat

[frgfm]

This PR introduces the following modifications:

• embed the guidelines in the system prompt for the chat
• on the code chat route, pull the guidelines of the authenticated user before sending the request to the model
• update the test fixture

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.53%. Comparing base (1539345) to head (62bc287).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #122      +/-   ##
==========================================
- Coverage   83.55%   83.53%   -0.02%     
==========================================
  Files          29       29              
  Lines         894      899       +5     
==========================================
+ Hits          747      751       +4     
- Misses        147      148       +1     

Flag	Coverage Δ
unittests	83.53% <100.00%> (-0.02%)	⬇️

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