refactor: apply SOLID principles to validator logic and remove magic strings/numbers

feat: enforce non-zero flow and add sample submission

feat: add CSV support for submissions and flow table visualization

clean up codebase: remove unused files, dependencies and simplify core UI logic

chore: final cleanup, update README and fix gitignore

fix(evaluation): collect all validation errors and generate valid baseline

feat(evaluation): add core LMMF validator for flow problem