Add package.json version fallback to release workflows

[ScottMorris]

Context

threshold's release-build.yml has a useful pattern: when triggered via workflow_dispatch without a manual tag, it reads the version from package.json:

version="$(node -p "require('./apps/threshold/package.json').version")"

This repo's publish-desktop.yml requires a release_tag input for workflow_dispatch. There's no fallback to read the version from the workspace's package.json.

Proposal

Add a package.json version fallback to the prepare-release job:

if [[ "${GITHUB_EVENT_NAME}" == "workflow_dispatch" ]]; then
  TAG="${{ inputs.release_tag }}"
  if [[ -z "${TAG}" ]]; then
    TAG="desktop-v$(node -p "require('./apps/desktop/package.json').version")"
  fi
fi

Apply the same pattern to build-android.yml for android-v* tags.

Acceptance Criteria

• workflow_dispatch inputs allow blank tag (fallback to package.json)
• Desktop publish workflow reads version from apps/desktop/package.json
• Android build workflow reads version similarly
• Tag-triggered releases still work as before