fix: review fixes + feat: imports, assertions, merge engine, per-package overrides

Review fixes (8 blocking issues):
- Extract ParseError to shared error.hpp (ODR fix)
- Remove dead package.cpp/package.hpp + tomlplusplus dep
- Safe parse_int() helper replacing crash-prone std::stoi
- consume_string() now accepts bare numbers and idents
- line_at() fixed for post-EOF line numbers
- Subcommand validation before file read in CLI
- KwService/KwAssert/KwImport added to consume_ident()
- root partition promoted to first-class BootBlock field

New features:
- Imports: imports = [...] with recursive merge resolution
- Assertions: assert { "msg" : field op value } in both parsers
- Merge engine: resolve_package() with features/config merge + force support
- Per-package overrides: /kappa/system/builds/<name>.kap
- .gitignore: added vcpkg_installed/ and kappa binary

src/main.cpp

@@ -48,24 +48,25 @@ static std::string read_file(const char* path) {
 static void handle_parse_error(const char* path,
                                std::string_view source,
                                const std::runtime_error& e) {
-    // ParseError format: "line:col: message"
     auto msg = std::string_view(e.what());
     auto first_colon = msg.find(':');
     auto second_colon = msg.find(':', first_colon + 1);
 
     if (first_colon != std::string_view::npos &&
         second_colon != std::string_view::npos) {
-        int line = std::stoi(std::string(msg.substr(0, first_colon)));
-        int col  = std::stoi(std::string(
-            msg.substr(first_colon + 1, second_colon - first_colon - 1)));
-        auto message = msg.substr(second_colon + 2); // skip ": "
+        try {
+            int line = std::stoi(std::string(msg.substr(0, first_colon)));
+            int col  = std::stoi(std::string(
+                msg.substr(first_colon + 1, second_colon - first_colon - 1)));
+            auto message = msg.substr(second_colon + 2);
 
-        cli::print_error(std::cerr, source,
-                         {path, line, col}, message,
-                         "check the syntax at this location");
-    } else {
-        std::cerr << "error: " << e.what() << '\n';
+            cli::print_error(std::cerr, source,
+                             {path, line, col}, message,
+                             "check the syntax at this location");
+            return;
+        } catch (const std::exception&) {}
     }
+    std::cerr << "error: " << e.what() << '\n';
 }
 
 int main(int argc, char* argv[]) {
@@ -86,6 +87,16 @@ int main(int argc, char* argv[]) {
         return 0;
     }
 
+    bool valid_subcommand = (subcommand == "parse-package")
+                         || (subcommand == "parse-config")
+                         || (subcommand == "validate");
+
+    if (!valid_subcommand) {
+        std::cerr << "error: unknown subcommand '" << subcommand << "'\n\n";
+        print_usage();
+        return 1;
+    }
+
     // Find the file argument (skip flags)
     const char* file_arg = nullptr;
     for (int i = 2; i < argc; ++i) {
@@ -145,7 +156,5 @@ int main(int argc, char* argv[]) {
         }
     }
 
-    std::cerr << "error: unknown subcommand '" << subcommand << "'\n\n";
-    print_usage();
-    return 1;
+    return 1; // unreachable
 }