feat: add kappa add and kappa remove subcommands

- kappa add <pkg> [version] — adds/updates package in system config
  packages{} block; creates config if it doesn't exist

- kappa remove <pkg> — removes package from config; idempotent
  (no error if package isn't present)

- Supports --root flag for custom KAPPA_ROOT

- User workflow: kappa add make && kappa rebuild
  No manual config editing needed.

src/main.cpp

@@ -53,6 +53,8 @@ Subcommands:
   list                    List installed packages
   rollback                Show available generations
   index        <dir>      Build an index.kap from .kap files in a directory
+  add          <pkg> [v]  Add a package to system config (optional version)
+  remove       <pkg>      Remove a package from system config
 
 Options:
   -h, --help              Show this help message
@@ -218,7 +220,9 @@ int main(int argc, char* argv[]) {
                          || (subcommand == "list")
                            || (subcommand == "fetch-package")
                            || (subcommand == "rollback")
-                           || (subcommand == "index");
+                           || (subcommand == "index")
+                           || (subcommand == "add")
+                           || (subcommand == "remove");
 
     if (!valid_subcommand) {
         std::cerr << "error: unknown subcommand '" << subcommand << "'\n\n";
@@ -227,6 +231,7 @@ int main(int argc, char* argv[]) {
     }
 
     const char* file_arg = nullptr;
+    const char* version_arg = nullptr;
     bool dry_run = false;
     for (int i = arg_start + 1; i < argc; ++i) {
         if (std::string_view(argv[i]) == "-h"
@@ -254,10 +259,14 @@ int main(int argc, char* argv[]) {
             continue;
         }
         if (!is_flag(argv[i])) {
+            if (file_arg == nullptr) {
                 file_arg = argv[i];
+            } else if (version_arg == nullptr) {
+                version_arg = argv[i];
                 break;
             }
         }
+    }
 
     if (subcommand == "list") {
         auto entries = install::read_installed();
@@ -320,6 +329,102 @@ int main(int argc, char* argv[]) {
         }
     }
 
+    if (subcommand == "add") {
+        if (file_arg == nullptr) {
+            std::cerr << "error: no package name specified\n";
+            return 1;
+        }
+        try {
+            auto config_path = std::filesystem::path(paths::system_dir()) / "config.kap";
+            dsl::SystemConfig cfg;
+
+            if (std::filesystem::exists(config_path)) {
+                auto src = read_file(config_path.c_str());
+                cfg = dsl::parse_system_config(src);
+            }
+
+            bool found = false;
+            for (auto& p : cfg.packages) {
+                if (p.name == file_arg) {
+                    found = true;
+                    if (version_arg != nullptr) {
+                        p.version = version_arg;
+                        std::cout << "updated " << file_arg
+                                  << " → version " << version_arg << "\n";
+                    } else {
+                        std::cout << file_arg << " already in packages\n";
+                    }
+                    break;
+                }
+            }
+
+            if (!found) {
+                dsl::PackageRef pref;
+                pref.name = file_arg;
+                if (version_arg != nullptr) {
+                    pref.version = version_arg;
+                }
+                cfg.packages.push_back(std::move(pref));
+                std::cout << "added " << file_arg;
+                if (version_arg != nullptr) {
+                    std::cout << " " << version_arg;
+                }
+                std::cout << "\n";
+            }
+
+            std::error_code ec;
+            std::filesystem::create_directories(paths::system_dir(), ec);
+            std::ofstream out(config_path);
+            if (!out) {
+                std::cerr << "error: cannot write " << config_path.string() << "\n";
+                return 1;
+            }
+            tools::format_config(out, cfg);
+            return 0;
+        } catch (const std::exception& e) {
+            std::cerr << "add error: " << e.what() << "\n";
+            return 1;
+        }
+    }
+
+    if (subcommand == "remove") {
+        if (file_arg == nullptr) {
+            std::cerr << "error: no package name specified\n";
+            return 1;
+        }
+        try {
+            auto config_path = std::filesystem::path(paths::system_dir()) / "config.kap";
+            if (!std::filesystem::exists(config_path)) {
+                std::cout << file_arg << " not found (no config)\n";
+                return 0;
+            }
+
+            auto src = read_file(config_path.c_str());
+            auto cfg = dsl::parse_system_config(src);
+
+            auto it = std::remove_if(cfg.packages.begin(), cfg.packages.end(),
+                [&](const dsl::PackageRef& p) { return p.name == file_arg; });
+
+            if (it == cfg.packages.end()) {
+                std::cout << file_arg << " not in packages\n";
+                return 0;
+            }
+            cfg.packages.erase(it, cfg.packages.end());
+            std::cout << "removed " << file_arg << "\n";
+
+            std::ofstream out(config_path);
+            if (!out) {
+                std::cerr << "error: cannot write " << config_path.string() << "\n";
+                return 1;
+            }
+            tools::format_config(out, cfg);
+            return 0;
+        } catch (const std::exception& e) {
+            std::cerr << "remove error: " << e.what() << "\n";
+            return 1;
+        }
+    }
+
     if (subcommand == "fetch-package") {
         if (file_arg == nullptr) {
             std::cerr << "error: no package name specified\n";