fix: enable Fedora repos and fix package availability in Hummingbird images

[maxamillion]

Summary

• Fixes container image build failures caused by missing packages in the Hummingbird repository.

Problem

The Hummingbird container images use a curated package repository that does not include many standard Fedora packages (protobuf-compiler, iptables, socat, rsync, curl, tar). Additionally, the hummingbird/curl:latest-builder image lacks curl and tar binaries, and the nvidia-container-toolkit stage fails SSL cert validation.

Fix

1. Enable Fedora repos — adds dnf install -y fedora-repos as the first step in stages that need packages outside the Hummingbird repo (rust-builder, cluster, CI image)
2. Replace curl builder stages — switches k9s and helm download stages from hummingbird/curl:latest-builder to core-runtime:latest-builder with curl, tar, gzip installed explicitly
3. Add ca-certificates to nvidia-container-toolkit stage to fix SSL errors when fetching the NVIDIA RPM repo

Testing

After merging, trigger all image builds:

gh workflow run "Build CI Image" --repo LobsterTrap/OpenShell --ref midstream
gh workflow run "Midstream Container Build" --repo LobsterTrap/OpenShell --ref midstream

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