⚡ Bolt: [performance improvement] Batch git branch deletion in PowerShell

[Cylae]

💡 What: Replaced the ForEach-Object loop calling git branch -D inside script.ps1 with an array pipeline collection that passes all candidate branch names as arguments to a single git branch -D invocation.
🎯 Why: PowerShell automatically expands arrays passed to native commands. By calling a native executable (like git) inside a loop, PowerShell spawns a new process on every iteration, causing significant overhead (N+1 bottleneck) that scales poorly with the number of open/merged branches.
📊 Impact: Reduces process creations from O(N) to O(1) for branch cleanup, significantly speeding up the script execution when cleaning a large number of branches.
🔬 Measurement: Verify by executing the script locally in an environment with hundreds of merged branches. The cleanup phase should complete nearly instantaneously instead of taking several seconds.

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PR created automatically by Jules for task 2987764051039700790 started by @Cylae

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