arrstack/nzbget: fix nonexistent image tag v26.2 -> version-v26.2 (#370)

The nzbget pod in namespace `arrstack` is stuck in `Init:ImagePullBackOff`.

## Why
The deployment pins `artifactapi.k8s.syd1.au.unkin.net/dockerhub/linuxserver/nzbget:v26.2` on both the `seed-config` initContainer and the main `nzbget` container. linuxserver does not publish a bare `v26.2` tag - the pull fails with:

```
failed to resolve reference ".../linuxserver/nzbget:v26.2": ... not found
Error: ImagePullBackOff
```

Confirmed against the artifactapi dockerhub mirror: `manifests/v26.2` -> HTTP 404. linuxserver version-pins nzbget under the `version-v<MAJOR>.<MINOR>` scheme, and the immutable date tags `26.2.<date>`. `manifests/version-v26.2` -> HTTP 200.

## Change
- Set both nzbget images (initContainer + main container) to `version-v26.2`, keeping nzbget on the intended 26.2 line and matching the version-pin convention used by the sibling sonarr (`4.0.19`) / radarr (`6.3.0`) deployments.

No other change. The `seed-config` init logic is unaffected - it already mirrors linuxserver's own init (`cp /app/nzbget/share/nzbget/nzbget.conf /config/nzbget.conf`), and since it seeds `/config/nzbget.conf` before the main container, linuxserver's init copy is skipped (no conflict). Instant-move download layout on the media PVCs is preserved.

## Validation
- `kustomize build --enable-helm apps/overlays/au-syd1/arrstack` renders cleanly (both images -> `version-v26.2`, no stale `v26.2`).
- `pre-commit run --files apps/base/arrstack/nzbget/deployment.yaml` passes (yamllint et al).

Scoped to `apps/base/arrstack/nzbget/deployment.yaml` only; the top-level `apps/base/arrstack/kustomization.yaml` was not touched (another agent is editing sonarr/radarr/prowlarr on a separate branch).

---------

Co-authored-by: unkin-agent <unkin-agent@users.noreply.git.unkin.net>
Reviewed-on: #370
Co-authored-by: Unkin Agent <unkin-agent@unkin.net>
Co-committed-by: Unkin Agent <unkin-agent@unkin.net>

apps/base/arrstack/nzbget/deployment.yaml

@@ -29,7 +29,7 @@ spec:
         # repeated option, and the grep guard keeps re-runs idempotent so admin
         # UI edits to the persisted /config/nzbget.conf survive restarts.
         - name: seed-config
-          image: artifactapi.k8s.syd1.au.unkin.net/dockerhub/linuxserver/nzbget:v26.2
+          image: artifactapi.k8s.syd1.au.unkin.net/dockerhub/linuxserver/nzbget:version-v26.2
           command:
             - sh
             - -c
@@ -81,7 +81,7 @@ spec:
               mountPath: /media/movies
       containers:
         - name: nzbget
-          image: artifactapi.k8s.syd1.au.unkin.net/dockerhub/linuxserver/nzbget:v26.2
+          image: artifactapi.k8s.syd1.au.unkin.net/dockerhub/linuxserver/nzbget:version-v26.2
           imagePullPolicy: IfNotPresent
           ports:
             - name: http