Add CLAUDE.md with codebase guidance

[diegokolling]

Summary

Adds a CLAUDE.md at the repo root to give future Claude Code sessions the big-picture context and commands they need to be productive quickly.

The file documents:

• The three interdependent components — backend/ (TS/Node API), frontend/ (Angular 20, dual-builds mempool.space + liquid.network), and rust/gbt/ (Rust getBlockTemplate compiled to a Node addon) — and how the backend's preinstall couples to the Rust build.
• Common commands for each component: build, run, lint, unit tests, running a single backend test, DB-backed integration tests, and Cypress E2E.
• Toolchain notes — Node v24.13.0 / npm 11.12.0 per .nvmrc/CI (the per-component READMEs still say Node 20.x), Rust required, separate node_modules per component.
• Backend architecture — index.ts server/cluster entry, the Esplora/Electrum/Core data-source abstract factory, repositories + migrations, background tasks, and the indexer.
• Frontend architecture — generated config (generate-config.js / update-config.js / themes), the BASE_MODULE mechanism behind the dual-site build, Angular serve "configurations" + proxy files, and i18n.
• Conventions & gotchas — most notably the custom local-rules/no-unhandled-await + no-floating-promises async-safety lint rules (the most common backend lint failure) and the ESLint 8-vs-9 split between backend and frontend.

Content was derived from the existing README.md files, package.json scripts, CI workflows, ESLint configs, and the source tree. No application code is touched.

https://claude.ai/code/session_01PmyRdk3wLvwauA5mHfKDHi

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