fix(config): recover cached git sources on detached head

[dcoric]

What

When a git-backed config source (configurationSources) pins a branch, the refresh cycle could fail: a plain git pull on the cached clone errors once the checkout is on a detached HEAD or the remote branch has moved. The cached repo then never recovers without manual deletion.

This change makes the refresh path branch-aware:

• the git env (GIT_TERMINAL_PROMPT=false, optional GIT_SSH_COMMAND) is now shared by clone, fetch, and pull, where previously only the initial clone used it — so authenticated refreshes work too
• with a pinned branch: git fetch --all --prune, then checkout, then git pull --ff-only origin <branch>
• without a pinned branch: plain git pull as before

Why a separate PR

Split out of #1532 per review feedback there — it's a standalone ConfigLoader fix, not part of the postgres sink.

Testing

test/ConfigLoader.test.ts gains coverage that a cached repository left on a detached HEAD (and on an unborn default branch) is recovered on the next refresh.

[netlify]

✅ Deploy Preview for endearing-brigadeiros-63f9d0 canceled.

Name	Link
🔨 Latest commit	815b838
🔍 Latest deploy log	https://app.netlify.com/projects/endearing-brigadeiros-63f9d0/deploys/6a2abf532bad8500083dedf4

[codecov]

Codecov Report

❌ Patch coverage is 56.25000% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.30%. Comparing base (8ac32ba) to head (815b838).

Files with missing lines	Patch %	Lines
src/config/ConfigLoader.ts	56.25%	14 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1587      +/-   ##
==========================================
- Coverage   85.51%   85.30%   -0.21%     
==========================================
  Files          83       83              
  Lines        7877     7896      +19     
  Branches     1312     1316       +4     
==========================================
  Hits         6736     6736              
- Misses       1114     1132      +18     
- Partials       27       28       +1     

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