Fix git clone error handling and consolidate implementations

[vrubezhny]

• Enhanced cloneRepository() in util/git.ts with comprehensive error handling for missing git executable
• Added try-catch around Git API access to prevent crashes
• Validate git executable path before spawning process
• Consolidated duplicate clone() function in createDeploymentLoader
• Removed duplicate CloneProcess interface, use CloneResult instead
• Changed from cp.exec to using centralized cloneRepository()
• Prevents "spawn git ENOENT" unhandled promise rejections in tests

Assisted-By: Claude Sonnet 4.5 noreply@anthropic.com

[codecov]

Codecov Report

❌ Patch coverage is 54.54545% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 47.72%. Comparing base (da60441) to head (749218f).
⚠️ Report is 1858 commits behind head on main.

Files with missing lines	Patch %	Lines
...ebview/create-deployment/createDeploymentLoader.ts	40.00%	3 Missing ⚠️
src/util/git.ts	66.66%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #5938       +/-   ##
===========================================
+ Coverage   32.37%   47.72%   +15.35%     
===========================================
  Files          85      106       +21     
  Lines        6505     9841     +3336     
  Branches     1349     2212      +863     
===========================================
+ Hits         2106     4697     +2591     
- Misses       4399     5141      +742     
- Partials        0        3        +3     

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