feat: add netssh version and --version

`netssh --version` used to be passed to ssh and failed with
"unknown option -- -". Release builds now embed the tag via
-X main.version; other builds fall back to the module build info.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.gitea/workflows/release.yml

@@ -34,7 +34,7 @@ jobs:
             out="dist/netssh_${GOOS}_${GOARCH}"
             echo "→ $out"
             CGO_ENABLED=0 GOOS=$GOOS GOARCH=$GOARCH \
-              go build -trimpath -ldflags="-s -w" \
+              go build -trimpath -ldflags="-s -w -X main.version=${GITHUB_REF_NAME}" \
               -o "$out" ./cmd/netssh
           done