refactor: move vantagectl to vantage-ctl

vantagectl/ becomes the root of gitea.hostxtra.co.uk/vantage/vantage-ctl.
The command keeps the name vantagectl; only the repository and the image
path change, to vantage/vantage-ctl.

chart-release.yml's render checks are repointed at the new image. The
chart itself has no default backup.image and fails loudly without one, so
an existing cluster keeps working until someone changes the value.

go.work stays, now with a single use ./server entry: without it a go.work
further up the developer's filesystem is picked up instead.

go.work.sum

@@ -1,6 +1,5 @@
 cloud.google.com/go/compute v1.25.1/go.mod h1:oopOIR53ly6viBYxaDhBfJwzUAxf1zE//uf3IB011ls=
 cloud.google.com/go/compute/metadata v0.3.0/go.mod h1:zFmK7XCadkQkj6TtorcaGlCW1hT1fIilQDwofLpJ20k=
-gitea.hostxtra.co.uk/vantage/vantage-shared v0.1.0/go.mod h1:dWjeOFLltQ8sv9Pnn1xRxGfWGgqa2fkG0esuaJLoPXQ=
 github.com/Intevation/gval v1.3.0/go.mod h1:xmGyGpP5be12EL0P12h+dqiYG8qn2j3PJxIgkoOHO5o=
 github.com/Intevation/jsonpath v0.2.1/go.mod h1:WnZ8weMmwAx/fAO3SutjYFU+v7DFreNYnibV7CiaYIw=
 github.com/VividCortex/ewma v1.2.0/go.mod h1:nz4BbCtbLyFDeC9SUHbtcT5644juEuWfUAUnGx7j5l4=
@@ -31,6 +30,7 @@ github.com/google/go-cmp v0.5.5/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/
 github.com/google/go-cmp v0.5.9/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
 github.com/hashicorp/errwrap v1.0.0/go.mod h1:YH+1FKiLXxHSkmPseP+kNlulaMuP3n2brvKWEqk/Jc4=
 github.com/hashicorp/go-multierror v1.1.1/go.mod h1:iw975J/qwKPdAO1clOe2L8331t/9/fmwbPZ6JB6eMoM=
+github.com/inconshreveable/mousetrap v1.1.0/go.mod h1:vpF70FUmC8bwa3OWnCshd2FqLfsEA9PFc4w1p2J65bw=
 github.com/josephburnett/jd/v2 v2.3.0/go.mod h1:0I5+gbo7y8diuajJjm79AF44eqTheSJy1K7DSbIUFAQ=
 github.com/josharian/intern v1.0.0/go.mod h1:5DoeVV0s6jJacbCEi61lwdGj/aVlrQvzHFFd8Hwg//Y=
 github.com/klauspost/cpuid/v2 v2.2.9/go.mod h1:rqkxqrZ1EhYM9G+hXH7YdowN5R5RGN6NK4QwQ3WMXF8=
@@ -42,6 +42,7 @@ github.com/package-url/packageurl-go v0.1.3/go.mod h1:nKAWB8E6uk1MHqiS/lQb9pYBGH
 github.com/pandatix/go-cvss v0.6.2/go.mod h1:jDXYlQBZrc8nvrMUVVvTG8PhmuShOnKrxP53nOFkt8Q=
 github.com/rivo/uniseg v0.4.7/go.mod h1:FN3SvrM+Zdj16jyLfmOkMNblXMcoc8DfTHruCPUcx88=
 github.com/russross/blackfriday v1.6.0/go.mod h1:ti0ldHuxg49ri4ksnFxlkCfN+hvslNlmVHqNRXXJNAY=
+github.com/russross/blackfriday/v2 v2.1.0/go.mod h1:+Rmxgy9KzJVeS9/2gXHxylqXiyQDYRxCVz55jmeOWTM=
 github.com/santhosh-tekuri/jsonschema/v5 v5.3.1/go.mod h1:uToXkOrWAZ6/Oc07xWQrPOhJotwFIyu2bBVN41fcDUY=
 github.com/shopspring/decimal v1.4.0/go.mod h1:gawqmDU56v4yIKSwfBSFip1HdCCXN8/+DMd9qYNcwME=
 github.com/spf13/cobra v1.8.1/go.mod h1:wHxEcudfqmLYa8iTfL+OuZPbBZkmvliBWKIezN3kD9Y=
@@ -67,6 +68,7 @@ golang.org/x/sys v0.41.0/go.mod h1:OgkHotnGiDImocRcuBABYBEXf8A9a87e/uXjp9XT3ks=
 golang.org/x/sys v0.46.0/go.mod h1:4GL1E5IUh+htKOUEOaiffhrAeqysfVGipDYzABqnCmw=
 golang.org/x/telemetry v0.0.0-20260625142307-59b4966ccb57/go.mod h1:3AWMyWHS+caVoiEXpiq6+tzKA40J4vQT3MYr80ZtQpc=
 golang.org/x/term v0.44.0/go.mod h1:7ze4MdzUzLXpSAoFP1H0bOI9aXDqveSvatT5vKcFh2Y=
+golang.org/x/term v0.45.0/go.mod h1:9aqxs0blBcrm/n0L9QW0aRVD+ktan8ssZromtqJC43w=
 golang.org/x/text v0.22.0/go.mod h1:YRoo4H8PVmsu+E3Ou7cqLVH8oXWIHVoX0jqUWALQhfY=
 golang.org/x/text v0.32.0/go.mod h1:o/rUWzghvpD5TXrTIBuJU77MTaN0ljMWE47kxGJQ7jY=
 golang.org/x/text v0.34.0/go.mod h1:homfLqTYRFyVYemLBFl5GgL/DWEiH5wcsQ5gSh1yziA=