build: suppress non-essential packages, fix dbus epoll, add git cache

- Suppress curl and git (non-essential for boot, build issues)
- D-Bus: disable epoll (-Depoll=disabled) for relibc compat
- Cookbook: revert skip-on-missing (broke sysroot install)
- Cache system: git-tracked pkgar in local/cache/pkgar/
- Rebuild progress: redox-driver-sys, iommu, kernel, kf6-ecm, dbus done

src/cook/cook_build.rs

@@ -602,10 +602,6 @@ fn build_deps_dir(
 
         let pkey_path = "build/id_ed25519.pub.toml";
         for (name, archive_path) in dep_pkgars {
-            if !archive_path.is_file() {
-                eprintln!("WARNING: dependency '{}' stage.pkgar missing at '{}' — rebuilding", name, archive_path.display());
-                continue;
-            }
             let tag_file = tags_dir.join(name.without_prefix());
             fs::write(&tag_file, "")
                 .map_err(|e| format!("failed to write tag file {}: {:?}", tag_file.display(), e))?;