Add final product polish: history export, observability pack, and frontend lint

[btcneves]

Summary

• History export CSV/JSON — adds GET /history/export.json and GET /history/export.csv with optional filters (source, success, since, until, limit), plus Export buttons in the Historical Dashboard (EN-US / PT-BR).
• Grafana + Prometheus observability pack — adds optional docker-compose.observability.yml with a pre-built Grafana dashboard covering real NodeScope metrics, plus make observability-up and make observability-down.
• Frontend ESLint + Prettier — adds ESLint v9 flat config and Prettier; CI now validates npm run lint, npm run format:check, and frontend build.
• Test count corrected — updates documentation from 54 to 80 Python unit tests where applicable, reflecting 71 prior tests plus 9 new export tests.
• Public documentation updated — updates PROJECT_STATUS, CHANGELOG, ROADMAP, README, and presentation docs to reflect the current implementation truthfully.

Validation

• python3 -m compileall api/ tests/ — OK
• python3 -m ruff check api/ tests/ — OK
• python3 -m ruff format --check api/ tests/ — OK
• docker compose config — valid
• docker compose -f docker-compose.yml -f docker-compose.observability.yml config — valid
• bash scripts/check-public-clean.sh — CLEAN (0 issues)
• TypeScript build — OK
• ESLint — OK, with 1 accepted warning: react-hooks/exhaustive-deps in ClusterMempoolPanel
• Prettier format:check — OK

Deferred / Not Included

• Screenshots — not generated in this cycle because Docker was not running in the current development environment. No fake screenshots were added.
• Demo video/GIF — not generated in this cycle because there was no graphical environment and Docker was unavailable. No fake video/GIF was added.

These items remain valid next steps and should be completed from a local environment with Docker and browser automation available.

Safety

• No private operational files included.
• No .env, secrets, tokens, API keys, wallets, local databases, or sensitive logs included.
• No internal development-tool references in public files.
• No direct push to main.
• Manual merge required.