qa: rely on SciMLTesting for rendered API coverage

[ChrisRackauckas-Claude]

Note

Please ignore this draft until it has been reviewed by @ChrisRackauckas.

What changed

• Remove MTK's repository-specific canonical_docs_entries rendered-API test.
• Remove the deprecated target_defined_modules JET override from run_qa.
• Require SciMLTesting 2.9, whose scoped rendered-doc check covers each @autodocs block directly.

The manual now relies on the standard SciMLTesting public API and rendered-document checks. The explicit reexport allowlist and genuine ExplicitImports/Aqua ownership exceptions remain unchanged.

This draft depends on SciMLTesting #51 being merged and registered as 2.9.0; its QA environment cannot resolve 2.9 before that release. It is intentionally separate from the JET scalability investigation documented in MTK issue #4958.

Verification

• Runic check on test/qa/qa.jl: passed.
• Typos on the changed QA files: passed.
• TOML parse of test/qa/Project.toml: passed.
• git diff --check: passed.

The full QA suite is deferred until SciMLTesting 2.9.0 is registered; running the old 2.8 harness here would falsely validate the removed bespoke rendered-doc coverage.