Task: Add working agreement for new tests to declare contract source and fidelity

[RtlZeroMemory]

Parent EPIC: #325

Problem:

The strategy will drift unless new tests are required to declare what contract they pin and at what fidelity.

Scope:

• Define the minimum declaration expected for new test work.
• Keep the rule small enough to apply consistently.
• Tie it back to behavior-first review and the test inventory process.

Done when:

• New test work has a clear working agreement for contract source and fidelity.
• The rule is practical enough to use during normal review.

Notes:

• This task should produce work that is reviewable against expected behavior, not current implementation shape.
• Keep outputs straight to the point and tied to repo code or repo process.

[RtlZeroMemory]

Implemented in PR #368: #368

What changed:

• added the new-test contract-source and fidelity rule to docs/dev/testing.md
• kept the wording short and reviewer-friendly
• left the existing pull-request template checklist in place as the PR-time reinforcement for the same expectation

What was verified:

• the rule now lives in an existing contributor-facing testing doc instead of a new process-doc area
• the PR template still reinforces the same review check

What was intentionally left out:

• no new internal docs area
• no extra contributor process document

Remaining ambiguity:

• none blocking this task; docs/dev/testing.md is already the stable home for test-author guidance