docs: add comprehensive troubleshooting section for Azul network upgrade

[erhnysr]

Summary

This PR adds a crucial Troubleshooting section to the base-v1-upgrade.mdx documentation.

Changes

• Added guidance for common migration issues including client version mismatches.
• Added P2P connectivity check instructions for the new Azul bootnodes.
• Clarified JWT authentication pathing for base-reth-node.

Why?

As the Azul upgrade approaches (Mainnet Early May), node operators need clear guidance on how to diagnose common setup failures during the transition from op-node to base-consensus.

[cb-heimdall]

🟡 Heimdall Review Status

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[erhnysr]

I've rebased this branch with the latest base:master to ensure full compatibility with the recent repository-wide directory restructuring. My specific changes are focused on adding the Troubleshooting section to the Azul upgrade guide to assist node operators during the upcoming transition. Ready for review!