fix: add /health, /metadata, /schema, /mcp endpoints + per-task graders

Final Compliance Fix: Add static tasks.json and explicit tasks reference in openenv.yaml for automated validator enumeration.

Compliance alignment: Use get_tasks() method and boolean grader flags for better OpenEnv discovery.

Refine task validation: Explicit grader refs and tasks property.

Fix task validation: Ensure 7 tasks with graders and get_tasks() method.

fix: resolve grader 500 error by ensuring ground_truth is set before scoring

fix: resolve Not enough tasks with graders validation error

Update tasks and grader metadata

Standard Template Restructuring: Passes openenv validate