chore: update mermaid diagram

[horsefacts]

Change Summary

Update contract docs + mermaid diagram

Merge Checklist

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• The PR title adheres to the conventional commits standard
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PR-Codex overview

This PR focuses on updating the documentation related to Ethereum Layer 1 and Layer 2 systems, specifically refining the structure of the diagrams and correcting section numbering in the docs/docs.md file.

Detailed summary

• Renamed subgraph Hubs to Snapchain in the diagram.
• Changed references from ETHL2 to OP in the diagram.
• Added Base subgraph to the diagram.
• Updated table of contents with corrected section numbers.
• Renamed sections for clarity, e.g., Key Registry to 1.4. Key Registry.
• Adjusted content to maintain consistency and clarity throughout the document.

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[github-actions]

Coverage after merging horsefacts/update-mermaid-diagram into main will be

100.00%

Coverage Report

File	Stmts	Branches	Funcs	Lines	Uncovered Lines
src
Bundler.sol	100%	100%	100%	100%
BundlerV1.sol	100%	100%	100%	100%
FnameResolver.sol	100%	100%	100%	100%
IdGateway.sol	100%	100%	100%	100%
IdRegistry.sol	100%	100%	100%	100%
KeyGateway.sol	100%	100%	100%	100%
KeyRegistry.sol	100%	100%	100%	100%
RecoveryProxy.sol	100%	100%	100%	100%
StorageRegistry.sol	100%	100%	100%	100%
TierRegistry.sol	100%	100%	100%	100%
src/abstract
EIP712.sol	100%	100%	100%	100%
Guardians.sol	100%	100%	100%	100%
Migration.sol	100%	100%	100%	100%
Nonces.sol	100%	100%	100%	100%
Signatures.sol	100%	100%	100%	100%
src/validators
SignedKeyRequestValidator.sol	100%	100%	100%	100%