Guard canonical docs against retired positioning terminology drift

[codeforester]

Summary

• Add a canonical positioning contract row to docs/contracts.md.
• Guard ten newcomer, contributor, agent, and library-facing surfaces against reintroducing the retired workspace control plane product phrase.
• Require the accepted local operating contract thesis and outcome loop in the appropriate introduction surfaces.
• Include the guard in tests/contracts/run.sh so future positioning drift fails with a named file and term.

Issue

Fixes #1761

Validation

• tests/contracts/run.sh
  • 43 GitHub workflow tests passed
  • 12 contract-hardening tests passed
  • remote-installer, workspace, inspection, release, stability, and BATS contract slices passed
• git diff --check
• Focused guard verifies the ten canonical surfaces and the required outcome loop.

Demo Impact

None. This is documentation policy and CI test coverage only.

Notes

This draft targets documentation/1760-20260725-core-doc-metadata as the preceding train branch. Retarget it to main after #1757 and #1760 are merged. Internal implementation terminology, license text, and historical assessment references remain intentionally outside the guard.