ci: commit Cargo.lock files for reproducible --locked builds

Fixes the `test` job failure (--locked rejected the absent lockfiles). sim has no
external deps; config-lint minimal — lockfiles are tiny and pin the toolchain deps.

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

.gitignore

@@ -1,7 +1,7 @@
 # Rust
 target/
 **/target/
-Cargo.lock
+# Cargo.lock IS committed (reproducible builds; CI uses --locked).
 
 # build artifacts (firmware/kernel objects are rebuilt from source)
 *.o