ci(tenant-registry): pin golangci-lint to v2.12.2 (Go 1.25 compatible)

go.mod's 'go 1.25.0' directive (auto-set by go mod tidy because
testcontainers-go v0.42.0 requires it) made the runner's bundled
golangci-lint (built on Go 1.24) refuse to load the config.
Pin to v2.12.2, the latest at time of writing, which is built on
Go 1.25.

Also: previous gofmt commit had subject 'style: gofmt -w' which our
custom commitlint regex rejects (style isn't in the type allowlist).
Squashed into this commit so the PR's commits all pass commitlint.

Refs: M4.1

.gitea/workflows/ci.yaml

@@ -72,7 +72,9 @@ jobs:
 
       - name: lint
         uses: golangci/golangci-lint-action@v6
-        with: { version: latest }
+        # Pin to a version built on Go 1.25 — the runner's bundled tool
+        # is Go 1.24 and refuses to lint a 1.25 module.
+        with: { version: v2.12.2 }
 
       - name: test
         # Coverage scoped to ./internal/... — cmd/server is the entrypoint