Migrate all production container runtime stages from Debian/Ubuntu
upstream to NVIDIA's hardened Ubuntu base image for supply chain
consistency.
- Dockerfile.ci: ubuntu:24.04 -> nvidia base
- Dockerfile.server: debian:bookworm-slim -> nvidia base (runtime stage)
- Dockerfile.base (sandbox): python:3.12-slim-bookworm -> nvidia base
with system Python 3.12 from Ubuntu Noble repos
- Dockerfile.cluster: convert from single-stage rancher/k3s to
multistage build extracting k3s artifacts onto nvidia base
Closes#244
## Summary
- Add `Provider` entity for managing 3p deps from a sandbox
- Add provider CRUD API/server persistence and new CLI workflows (`nav provider create/get/list/update/delete`), including `--from-existing` laptop discovery.
- Integrate providers into sandbox create flow: infer from command (`-- claude`), support repeatable `--provider <type>`, prompt before auto-create, and allow manual in-sandbox setup.
- Add a dedicated `navigator-providers` crate with per-provider modules and mockable discovery test helpers.
## Key UX Changes
- `nav sandbox create --provider gitlab -- claude`
- Missing provider prompt now asks before creating from local state.
- `nav provider list --names` for scripting/cleanup.
## Test Plan
- `mise run cluster:deploy`
- `mise run test:e2e:sandbox`
- `mise run pre-commit`
Closes#19Closes#22Closes#11
Piotr Mlocek