fix: oracle review fixes — resolver exit code, dead include, pointer compose

- Exit code: plan.missing.empty() ? 0 : 1 (was always returning 0)
- Removed dead <algorithm> include from plan.cpp
- BuildStep now composes config::ResolvedPackage instead of duplicating
  features/config fields; PackageDef stored as const pointer

src/main.cpp

@@ -270,9 +270,9 @@ int main(int argc, char* argv[]) {
             for (auto& step : plan.steps) {
                 std::cout << "  " << step.name << " (" << step.dependencies.size()
                           << " deps";
-                if (!step.features.empty()) {
+                if (!step.resolved.features.empty()) {
                     std::cout << ", features:";
-                    for (auto& [k, f] : step.features) {
+                    for (auto& [k, f] : step.resolved.features) {
                         if (f.enabled && !f.flag.empty()) {
                             std::cout << " " << k;
                         }
@@ -280,7 +280,7 @@ int main(int argc, char* argv[]) {
                 }
                 std::cout << ")\n";
             }
-            return plan.steps.empty() && plan.missing.empty() ? 0 : 0;
+            return plan.missing.empty() ? 0 : 1;
         } catch (const std::runtime_error& e) {
             handle_parse_error(file_arg, source, e);
             return 1;