Add scientific result contracts

[rajeeja]

Summary

• expose structured scientific status and postcondition fields on the MCP analysis front door
• propagate UXarray warning state into agent-readable vector-calculus results
• add semantic regression tests for result contracts
• scope pytest collection to the tracked tests directory so local archival outputs are not collected as project tests

Verification

• uv run pytest: 421 passed, 4 skipped
• uv run pre-commit run --all-files: all hooks passed

Scope

This PR contains only MCP implementation, tests, and pytest configuration. It intentionally excludes paper drafts, evaluation protocols, experiment artifacts, facility-local configuration, and site-specific paths.