docs: rewrite CLAUDE.md for Seismic fork

[mHaines9219]

Summary

• Rewrites CLAUDE.md from the generic upstream REVM version to be Seismic-fork-specific
• Adds platform-specific build instructions (macOS/Linux) with verified system deps (GMP)
• Documents the seismic crate, confidential storage opcodes, privacy precompiles, and semantic test runner
• Adds troubleshooting table with real issues encountered during build/test
• All build commands, test commands, and lint checks were run and verified on macOS

Test plan

• cargo build --workspace passes
• cargo test --workspace passes (~400 tests, 0 failures)
• cargo fmt --all --check passes
• RUSTFLAGS="-D warnings" cargo check passes
• Strict clippy on seismic-revm passes
• cargo run -p revme -- --help outputs expected subcommands

[cdrappi]

reorganized in #195