renovate: termix — strip -tag suffix from GitHub release tag_names

Verified with the GitHub Releases API for Termix-SSH/Termix that the
actual `tag_name` field is `release-X.Y.Z-tag` (with a `-tag` suffix),
even though the release `name` is `release-X.Y.Z`. Renovate's
github-releases datasource keys off `tag_name`, so the regex versioning
correctly rejects all candidates as invalid:

  INFO: Found no results from datasource that look like a version
        (dependency=Termix-SSH/Termix)

The docker image at ghcr.io/lukegus/termix uses the short form
(`release-X.Y.Z`, no suffix), which is what the manifest also has.

Fix: add `extractVersionTemplate: ^(?<version>release-\d+\.\d+\.\d+)`
which Renovate applies to each candidate from the datasource BEFORE
the versioning regex sees it. tag_names `release-2.3.2-tag` become
`release-2.3.2`, the regex versioning parses them, comparison works,
and Renovate writes the short form back to the manifest -- which is
the correct tag at the ghcr.io registry.

(extractVersion is NOT applied to currentValue, but currentValue already
is in the short form, so no normalization needed there.)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

admin-system/renovate.yaml

@@ -52,7 +52,7 @@ data:
       },
       "customManagers": [
         {
-          "description": "termix uses a release-X.Y.Z prefixed tag. extractVersion + loose doesn't work because Renovate validates the raw currentValue BEFORE applying extractVersion. Using regex versioning (which parses the prefixed value directly) sidesteps the pre-check. Datasource redirected to GitHub Releases at Termix-SSH/Termix so the 3-day stability gate has real timestamps to work with.",
+          "description": "termix: docker image tag is `release-X.Y.Z` but the upstream GitHub release tag_name is `release-X.Y.Z-tag` (different from the release name). regex versioning parses currentValue (no -tag); extractVersion strips the -tag suffix from candidate tag_names so they normalize to the same shape Renovate writes back to the manifest.",
           "customType": "regex",
           "managerFilePatterns": ["/termix-system/.+\\.ya?ml$/"],
           "matchStrings": [
@@ -60,7 +60,8 @@ data:
           ],
           "datasourceTemplate": "github-releases",
           "packageNameTemplate": "Termix-SSH/Termix",
-          "versioningTemplate": "regex:^release-(?<major>\\d+)\\.(?<minor>\\d+)\\.(?<patch>\\d+)$"
+          "versioningTemplate": "regex:^release-(?<major>\\d+)\\.(?<minor>\\d+)\\.(?<patch>\\d+)$",
+          "extractVersionTemplate": "^(?<version>release-\\d+\\.\\d+\\.\\d+)"
         }
       ],
       "packageRules": [