Migrate default branch from `master` to `main`

[ravi-prakash-v]

📌 Description

The repository currently uses the master branch as its default. To align with modern, inclusive standards and GitHub’s default conventions, we need to:

• Officially deprecate master
• Transition to main as the new default branch
• Update all references across the repo and community workflows

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🎯 Rationale

• Inclusivity: Industry-wide shift to using main instead of master.
• Consistency: Aligns Beckn Protocol repos with open-source best practices.
• Compatibility: Many CI/CD and automation tools expect main as the default.

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✅ Tasks

• Change default branch in GitHub repository settings from master → main.

• Ensure main is protected with the same branch protection rules as master.

• Update references to master in:

  • Documentation files
  • CI/CD configurations
  • Contribution guidelines
  • Governance references

• Notify community via Announcement (see linked PR/Discussion).

• Add redirects/aliases where necessary to avoid broken links.

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🔄 Community Instructions

Contributors are requested to:

• Update local branches (git branch -m master main).
• Rebase any open PRs onto main.
• Update Issues, Discussions, and documentation references pointing to master.

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📎 References

• GitHub guidance on renaming branches

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🔔 Impact: Medium — Requires community coordination but no breaking changes to specifications.