feat: allow branch name derivation from base branch for namespacing

[dvvaliya369]

Summary

Implements the ability to derive the target branch name from the base branch, enabling "namespacing" of generated pull requests based on their target branch.

Changes Made

• Added support for deriving branch names from base branch references
• Enables automated code generation workflows to create PRs against multiple branches
• Allows bots to namespace pull requests based on their target branch

Why This Change

This feature addresses the need for code generation workflows where:

• Code changes trigger automated codegen jobs
• PRs need to be opened against multiple branches
• Each PR should be namespaced to its target branch for better organization

Fixes #3668

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Agent: blackbox
Model: blackboxai/blackbox-pro