phase-21.9: add De‑Rust roadmap + phase plan; stage archive script for Rust LLVM backend (no move yet)

tools/de_rust/archive_rust_llvm_backend.sh

@@ -0,0 +1,30 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+ROOT="$(cd "$(dirname "$0")/../.." && pwd)"
+SRC_DIR="$ROOT/src/backend/llvm"
+DST_DIR="$ROOT/archive/rust-llvm-backend/llvm"
+RESTORE_MD="$ROOT/archive/rust-llvm-backend/RESTORE.md"
+
+echo "[info] De‑Rust Phase‑0: archive Rust LLVM backend"
+
+if [ ! -d "$SRC_DIR" ]; then
+  echo "[warn] src/backend/llvm not found; nothing to do" >&2
+  exit 0
+fi
+
+mkdir -p "$(dirname "$DST_DIR")"
+git mv "$SRC_DIR" "$DST_DIR"
+
+cat > "$RESTORE_MD" <<'EOF'
+# RESTORE — Rust LLVM backend
+
+To restore the archived backend back to the original location:
+
+  git mv archive/rust-llvm-backend/llvm src/backend/
+
+Rationale: Python llvmlite is the primary LLVM path. The Rust backend was deprecated and archived as part of the De‑Rust Phase‑0.
+EOF
+
+echo "[done] Archived to archive/rust-llvm-backend/. Review and commit when ready."
+