Unify root agent files into AGENTS.md

[masih]

Update root CLAUDE.md file to point to AGENTS.md, standardising on tree agent files.

[cursor]

PR Summary

Low Risk
Documentation-only reorganization with no application or build logic changes.

Overview
Makes AGENTS.md the single canonical root guide for agents and contributors, and turns CLAUDE.md into a thin wrapper that states edits belong in AGENTS.md (and nested package guides) and pulls content in via @AGENTS.md.

The expanded AGENTS.md adds repo context (Sei chain, Go 1.25.6), documents nested AGENTS.md paths (evmrpc/, x/evm/, sei-tendermint/), and consolidates gofmt, make lint / build / install, test sharding, golangci-lint / CI workflow references, and a pointer to benchmark/CLAUDE.md—material that previously lived only in CLAUDE.md (formatting + benchmarking).

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[github-actions]

The latest Buf updates on your PR. Results from workflow Buf / buf (pull_request).

Build	Format	Lint	Breaking	Updated (UTC)
✅ passed	✅ passed	✅ passed	✅ passed	Jun 15, 2026, 10:41 AM

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 58.37%. Comparing base (fdd2b68) to head (c91c04a).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3589      +/-   ##
==========================================
- Coverage   59.23%   58.37%   -0.87%     
==========================================
  Files        2214     2140      -74     
  Lines      183389   174842    -8547     
==========================================
- Hits       108636   102060    -6576     
+ Misses      64967    63697    -1270     
+ Partials     9786     9085     -701     

Flag	Coverage Δ
sei-db	70.41% <ø> (ø)
sei-db-state-db	?

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see 74 files with indirect coverage changes

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