refactor(core): DI-ready Pipeline; add registry + YAML factory + typed trace/result

fix(pipeline): allow optional schema_preview in run() for better typing compatibility with benchmarks

feat(safety): harden SQL validation (multi-CTE, recursive WITH, unicode normalization, precise errors, EXPLAIN gate)

tests green: fix pipeline reference in router and adjust verifier logic for aggregation & error handling

fix(pipeline): align backend-frontend schema and stabilize SQL flow

build(mypy): fix type errors and add safety guards for None values

style: fix Ruff issues (F401 unused import, E741 ambiguous var)

style: format code with ruff

refactor: unify pipeline output via FinalResult model

Fix some typo

style: format code with ruff

style: format code with ruff

init: NL2SQL Copilot base with API and Dockerfile