ci: run the full source quality gate on pull requests

.github/scripts/README.md

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+# Source PR CI evidence
+
+`ci.yml` runs the existing `cargo xtask ci` gate on opened, synchronized,
+reopened and ready-for-review PRs, without source/path or draft filters, plus main
+pushes and manual dispatch. The existing platform packaging triggers are unchanged.
+The read-only hosted Linux job tests the PR merge result and records both head
+and checkout identities. No PR-target execution or signing/deployment credentials
+are used. The 150-minute cold-build limit is provisional for this new job layout.
+
+The runner installs Mesa Lavapipe and probes its Vulkan adapter. A failed probe
+does not prevent CPU gates from running, but fails the final coverage report.
+`RUST_TEST_NOCAPTURE=1` exposes the existing GPU tests' adapter/parity/skip messages.
+The reporter requires a successful gate, executed Rust tests and positive GPU
+evidence; runtime no-adapter skips fail acceptance. Intentionally ignored platform
+cases are counted/reported separately. Complete logs and source identity are saved
+as artifacts. Software Vulkan coverage does not qualify physical GPU drivers,
+other operating systems or tests deliberately ignored on Linux.
+
+Run the report regression tests with
+`python3 -m unittest discover -s .github/scripts -p 'test_*.py' -v`.
+Trigger simulation and fixture tests do not prove GitHub events or runner images
+work: after approved publication/landing, inspect actual PR run URLs and results,
+including a ready-for-review event, before requiring the new check for merges.