[AIR-3027] qs: IamInMyBranch fucntionality is duplicated in few places

[host6]

AIR-3027 qs: IamInMyBranch fucntionality is duplicated in few places
https://untill.atlassian.net/browse/AIR-3027

[augmentcode]

🤖 Augment PR Summary

Summary: This PR deduplicates the “am I on main?” branch-detection logic across the QS CLI.

Changes:

• Replaced the old IamInMainBranch helper with GetCurrentBranchInfo, returning current branch, main branch, and a precomputed isMain flag
• Refactored callers (gitcmds.Download, commands.Dev, commands.U) to use the new helper instead of repeating GetCurrentBranchName + GetMainBranch + EqualFold
• Added an archived uspec implementation note documenting the refactor plan and verification steps

Technical Notes: Centralizing the main-branch check reduces drift between commands and ensures consistent error wrapping for main-branch detection failures.

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[augmentcode]

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