feat: system config DSL, services, CLI with rustc diagnostics

- System config parser (system/packages/services/boot/users blocks)
- Boot block: kernel, init, efi, swap, bootloader, root partition
- System-wide features, rollback config, swap partition
- Service block: per-init variants (runit, s6, etc.), system init selection via boot.init
- Feature-gated dependencies, config values accept numbers/bools/strings
- CLI: parse-package, parse-config, validate subcommands
- Rustc-style error diagnostics with source context, carets, help text
- Diagnostic module with ANSI color output

src/dsl/lexer.cpp

@@ -19,6 +19,7 @@ static const std::unordered_map<std::string_view, TokenType> keywords = {
     {"license",  TokenType::KwLicense},
     {"patches",  TokenType::KwPatches},
     {"env",      TokenType::KwEnv},
+    {"service",  TokenType::KwService},
     {"prepare",  TokenType::KwPrepare},
     {"build",    TokenType::KwBuild},
     {"check",    TokenType::KwCheck},
@@ -51,6 +52,7 @@ std::string_view token_name(TokenType type) {
     case TokenType::KwLicense:  return "license";
     case TokenType::KwPatches:  return "patches";
     case TokenType::KwEnv:      return "env";
+    case TokenType::KwService:  return "service";
     case TokenType::KwPrepare:  return "prepare";
     case TokenType::KwBuild:    return "build";
     case TokenType::KwCheck:    return "check";