docker: second review pass fixes

- Dockerfile: lift numba past vllm's 0.61.2 pin after the numpy>=2.4
  re-upgrade; 0.61.2 refuses numpy 2.3+ at import time and the stack
  cannot move numpy down. Verified numba 0.65 + numpy 2.4.6 + vllm
  import cleanly together.
- docker-publish.yml: resolve UNSLOTH_ZOO_REF in a step that mirrors
  the pushed tag only when the tag exists in unsloth-zoo (the zoo
  currently cuts no tags, so blind mirroring broke every tag publish);
  falls back to main.
- Dockerfile.studio: Studio venv stays on cu128 for arm64 too, matching
  the base venv (cu130 wheels would lift the driver floor to 580+), and
  gets the same NVRTC cu13 swap for DGX Spark / GB10 sm_121 support.
- docker_confirm.sh: do not drop to CPU mode when docker info lacks a
  nvidia runtime entry; CDI installs and Docker Desktop WSL2 expose
  GPUs without one. The phase 3 --gpus probe is now the authority.
- docker_confirm.ps1: GPU selector built as an args array; comma device
  lists get version-aware CSV quoting (native arg passing changed in
  PowerShell 7.3).
- studio_launch.sh: no fixed Jupyter default password; generate a
  random one and print it when JUPYTER_PASSWORD is unset. Env snapshot
  for SSH sessions now written via shlex.quote instead of sed so
  values with quotes or command substitution cannot break or inject
  into /etc/profile.d.
- install.ps1: honour UNSLOTH_TORCH_INDEX_FAMILY like install.sh does.

.github/workflows/docker-publish.yml

@@ -111,6 +111,24 @@ jobs:
         with:
           images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
 
+      # Mirror the unsloth tag into the zoo ONLY when that tag actually
+      # exists there. unsloth's v* tags are Studio releases the zoo never
+      # cuts (the zoo repo currently has no tags at all), so blindly
+      # mirroring github.ref_name made every tag publish fail inside the
+      # Dockerfile's zoo install.
+      - name: Resolve unsloth-zoo ref
+        id: zoo_ref
+        run: |
+          REF="${{ github.event.inputs.unsloth_zoo_ref }}"
+          if [ -z "$REF" ] && [ "${{ startsWith(github.ref, 'refs/tags/') }}" = "true" ]; then
+              if git ls-remote --exit-code --tags https://github.com/unslothai/unsloth-zoo \
+                  "refs/tags/${{ github.ref_name }}" >/dev/null 2>&1; then
+                  REF="${{ github.ref_name }}"
+              fi
+          fi
+          echo "ref=${REF:-main}" >> "$GITHUB_OUTPUT"
+          echo "unsloth-zoo ref: ${REF:-main}"
+
       - name: Build and push (per-arch by digest)
         id: build
         uses: docker/build-push-action@v6
@@ -134,12 +152,11 @@ jobs:
             # scheduled runs: bake the triggering commit SHA. Falls back
             # to `main` for any other event class.
             UNSLOTH_REF=${{ github.event.inputs.unsloth_ref || (startsWith(github.ref, 'refs/tags/') && github.ref_name) || github.sha || 'main' }}
-            # UNSLOTH_ZOO_REF mirrors the tag case (unsloth-zoo cuts the same
-            # release tag, e.g. 2026.5.8, alongside unsloth) so release-tag
-            # images install a matched zoo. SHA-based branch pushes can't be
-            # mirrored -- the SHA doesn't exist in the zoo repo -- so they
-            # fall through to `main`. Workflow-dispatch can override.
-            UNSLOTH_ZOO_REF=${{ github.event.inputs.unsloth_zoo_ref || (startsWith(github.ref, 'refs/tags/') && github.ref_name) || 'main' }}
+            # UNSLOTH_ZOO_REF comes from the resolve step above: explicit
+            # workflow-dispatch input, else the pushed tag IF the zoo repo
+            # has it, else `main`. SHA-based branch pushes always fall to
+            # `main` -- the SHA doesn't exist in the zoo repo.
+            UNSLOTH_ZOO_REF=${{ steps.zoo_ref.outputs.ref }}
 
       # Stash the per-arch digest as an artifact for the merge job to pick up.
       # Filenames need to be unique across the matrix; `platform` contains a