Add Cargo workspace, crate skeletons and the gate

Implemented-By: Laguna S 2.1 (OpenCode)

scripts/check-lines.sh

@@ -0,0 +1,14 @@
+#!/bin/sh
+# Fails if any *.rs file under ROOT/crates has more than 500 lines.
+# Files under any target/ directory are ignored. Test files count.
+ROOT="${1:-.}"
+
+bad=$(find "$ROOT/crates" -type f -name '*.rs' ! -path '*/target/*' \
+    -exec awk 'END { exit !(NR > 500) }' {} \; -print 2>/dev/null)
+if [ -n "$bad" ]; then
+    echo "$bad" | while read -r f; do
+        [ -n "$f" ] && echo "check-lines: $f" >&2
+    done
+    exit 1
+fi
+exit 0