docs: add deployment guide

[tabathad]

Part of #1325, complements #1335.

Adds a deployment guide covering:

• Prerequisites
• Quick start walkthrough
• Docker deployment
• Git client configuration
• Production considerations

Also adds the deployment page to the docs sidebar.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.35%. Comparing base (2150064) to head (24eb8e2).
⚠️ Report is 36 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1385      +/-   ##
==========================================
- Coverage   81.35%   81.35%   -0.01%     
==========================================
  Files          65       65              
  Lines        4639     4649      +10     
  Branches      792      792              
==========================================
+ Hits         3774     3782       +8     
- Misses        850      852       +2     
  Partials       15       15              

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