ci: GitHub Actions pipeline — cargo test + llvm-cov + badges (P5 host-testable jobs)

test job runs cargo test across sim + config-lint and cargo-llvm-cov line coverage
on the sim crate; badges job renders loc/tests/coverage shields on push to bringup
([skip ci] + paths-ignore loop guard). mcdc/bench/kernel-build jobs land with
P2/P4/P1. README carries the CI + badge row.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017wB8KB3MMQztRDXCMCkPrf

.github/badges/coverage.svg

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