docs: clarify ownership and cleanup review guidance

Clarify structural parsing, admitted facts and freshness, useful facade and compatibility responsibilities, immutable JSON proof, and partial Evidence retention. Document fixture cleanup ownership, semantic fault injection and the limits of static checks; extend the existing PR owner hint. Correct the session-record architecture label.

Validation: docs:check (including nine README consistency tests), rendered docs:build with link validation, touched Markdown formatting and git diff --check passed. Source and installed Vitest cleanup behavior were reviewed. No runtime behavior changed.

.github/pull_request_template.md

@@ -36,6 +36,9 @@ unchecked. Maintainers can help resolve open questions.
 Use "none" or "not applicable" only when established. -->
 
 - Semantic owner and earliest changed stage:
+  <!-- Name the producer of parsed facts or resources and its affected consumers.
+  Summarize superseded paths removed and any distinct policy, lifecycle,
+  lazy-loading, or compatibility responsibility retained. -->
 - Contribution scope fit and linked maintainer decision:
 - CLI and MCP/tool-catalog contract:
 - Provider, bridge, target-format, or platform compatibility: