Add integration test example and project rename script

tests/greet.rs shows the tests/ convention alongside the existing
inline unit test in src/lib.rs, so both standard locations are covered.

scripts/rename-project.sh replaces the "rust_template" placeholder
throughout Cargo.toml, flake.nix, nix/rust.nix, src/main.rs,
benches/greet.rs, and tests/greet.rs, then regenerates Cargo.lock.
Verified in a scratch copy: renamed crate builds, tests pass, and the
Nix package builds and runs correctly.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018ALEXkc7pTro7tF1WcUuKb

scripts/rename-project.sh

@@ -0,0 +1,54 @@
+#!/usr/bin/env bash
+# Renames the "rust_template" placeholder throughout the project to a
+# real crate name. Run from anywhere; it locates the repo root itself.
+set -euo pipefail
+
+old_name="rust_template"
+
+usage() {
+  echo "Usage: $0 <new_name>" >&2
+  echo "  <new_name> must be a valid snake_case Rust crate name (e.g. my_project)" >&2
+  exit 1
+}
+
+[[ $# -eq 1 ]] || usage
+new_name="$1"
+
+if ! [[ "$new_name" =~ ^[a-z][a-z0-9_]*$ ]]; then
+  echo "error: '$new_name' is not a valid snake_case crate name" >&2
+  exit 1
+fi
+
+if [[ "$new_name" == "$old_name" ]]; then
+  echo "already named '$old_name', nothing to do"
+  exit 0
+fi
+
+root="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+cd "$root"
+
+files=(
+  Cargo.toml
+  flake.nix
+  nix/rust.nix
+  src/main.rs
+  benches/greet.rs
+  tests/greet.rs
+)
+
+for f in "${files[@]}"; do
+  [[ -f "$f" ]] || continue
+  sed -i.bak "s/${old_name}/${new_name}/g" "$f"
+  rm -f "${f}.bak"
+done
+
+if command -v cargo >/dev/null 2>&1; then
+  cargo generate-lockfile
+else
+  echo "warning: cargo not on PATH — run 'cargo generate-lockfile' yourself (e.g. inside 'nix develop')" >&2
+fi
+
+echo "Renamed '${old_name}' -> '${new_name}'."
+echo
+echo "Review the diff (git diff), then optionally rename the project directory:"
+echo "  cd .. && mv $(basename "$root") ${new_name}"

tests/greet.rs

@@ -0,0 +1,6 @@
+use rust_template::greet;
+
+#[test]
+fn greets_by_name() {
+    assert_eq!(greet("integration"), "Hello, integration!");
+}