release: mark v0.* tags as prerelease per SemVer convention

Pre-1.0 releases get the prerelease flag in Gitea — pre-1.0 means
public API may break between minors (SemVer permits this), so these
shouldn't display as stable releases.

Computed from $TAG via `case` so the flag auto-flips to false when
v1.0.0 lands; no further workflow change needed at that point.

  case "$TAG" in
      v0.*) prerelease=true ;;
      *)    prerelease=false ;;
  esac

Passed to jq via --argjson (not --arg) so it stays a JSON boolean
rather than the string "true" / "false".

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

.gitea/workflows/release.yml

@@ -164,12 +164,18 @@ jobs:
             in_section
           ' "$GITHUB_WORKSPACE/CHANGELOG.md")
 
+          # Pre-1.0 tags are prerelease per SemVer convention.
+          case "$TAG" in
+              v0.*) prerelease=true ;;
+              *)    prerelease=false ;;
+          esac
+
           # Create the release (or get the existing one for this tag)
           release_json=$(curl -fsSL -X POST "$api/repos/$REPO/releases" \
               -H "Authorization: token $GITEA_TOKEN" \
               -H 'Content-Type: application/json' \
-              -d "$(jq -n --arg tag "$TAG" --arg name "$TAG" --arg body "$body" \
-                       '{tag_name:$tag,name:$name,body:$body,draft:false,prerelease:false}')" \
+              -d "$(jq -n --arg tag "$TAG" --arg name "$TAG" --arg body "$body" --argjson pre "$prerelease" \
+                       '{tag_name:$tag,name:$name,body:$body,draft:false,prerelease:$pre}')" \
               || curl -fsSL "$api/repos/$REPO/releases/tags/$TAG" \
                   -H "Authorization: token $GITEA_TOKEN")
           rid=$(echo "$release_json" | jq -r .id)