fix: restore UI, add /tasks /grade, clamp scores to (0.05, 0.95)

Massive Rewrite: Rebuilt Phase 2 standalone validation constraints perfectly mapped to 0.05-0.95

Rewrite environment, app endpoints, and openenv.yaml for Phase 2 validation

Fix Phase 2 issue: explicitly define tasks and graders in openenv.yaml

chore: update project descriptions to reflect SQL-RL branding in openenv.yaml, pyproject.toml, and README.md

hf done

hf issues now fixed

feat: implement SQL agent environment with OpenEnv integration, SQLite management, and automated task grading