CM-4: adopt release-rule semantics as working assumption (operator decision)

[lann]

Operator decision: proceed under the assumption that the wasmtime/wast-corpus semantics (entry-gating ends at resolution) becomes the spec for CM-4.

The runtime already implements it (annotated divergences in runtime/src/task/mod.ts, exec/boundary.ts, jspi/bridge.ts; contracts/intrinsics.md already records both supersedes spots). This PR adds the missing policy layer so future tracks don't 'correct' the runtime back toward definitions.py:

• architecture.md SS1: the tie-breaker clause gains its bounded exception — where definitions.py contradicts the spec repo's own wast corpus AND wasmtime implements the corpus side, the corpus semantics is the working assumption, recorded as a named CM-N finding, flipping back if upstream adjudicates otherwise. Bare wasmtime behavior with no corpus backing still never supersedes the reference.
• upstream-component-model-repo-findings.md CM-4: status records the adopted assumption, its implementation sites, and the flip-back trigger.

Docs-only.