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

examples/foo.kap

@@ -59,6 +59,20 @@ package "foo" {
         CFLAGS  ?= "-g"
     }
 
+    service {
+        runit {
+            exec  = "/usr/bin/foo --daemon"
+            type  = "forking"
+            user  = "foo"
+        }
+        s6 {
+            exec  = "/usr/bin/foo"
+            type  = "longrun"
+            ports = [80, 443]
+            user  = "foo"
+        }
+    }
+
     prepare {
         patch "fix-build.patch"
     }