docs: refine contract upgrade guide with explicit strategy and rollback procedures

[najeebullahii]

Closes #310

Overview

This PR addresses Issue #310 by refining the existing CONTRACT_UPGRADE_GUIDE.md to use straightforward, action-oriented, and contributor-friendly language.

What's Changed

The documentation has been updated to explicitly cover the four required core areas:

• Upgrade Strategy: Clear, direct guidelines on preserving state and interface safety.
• Deployment Sequence: A practical, sequential checklist for local builds, testnet staging, and verification.
• Common Risks: Highlighted major smart contract pitfalls including storage collisions and authorization failures.
• Rollback Recommendations: Added structured procedures to safely recover from live upgrade failures or regressions.

Verification

• Reviewed file structure and content layout to ensure self-contained readability for any incoming repository contributor.

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