fix(app-proxy): add timeout to prevent git process accumulation

[dmaizel]

What

Add timeout configuration to all git operations to automatically kill hanging git processes and prevent "cannot fork()" errors caused by process limit exhaustion.

• Create reusable createGitInstance() helper function that wraps simpleGit() with timeout configuration (5 minutes)
• Replace all direct simpleGit() calls with createGitInstance() to ensure timeout is always applied
• Prevents child processes (like git-remote-https) from accumulating when operations hang or take too long

This addresses the issue where app-proxy reaches the process limit (9222/9222) after running for extended periods, causing all git operations to fail with "Resource temporarily unavailable" errors.

Why

Notes

[dmaizel]

/e2e