Fix empty tag in dispatched Windows builds

The workflow_dispatch input was accessed as github.event.inputs.tag
which can be empty depending on the Gitea runner. Now tries both
inputs.tag (modern syntax) and github.event.inputs.tag as fallback,
with a final fallback to the latest matching git tag.

Also switched Windows Determine-tag steps from PowerShell to bash
(via Git Bash) for consistency with the other platforms.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitea/workflows/build-app-macos.yml

@@ -17,7 +17,10 @@ jobs:
       - name: Determine tag
         id: tag
         run: |
-          TAG="${{ github.event.inputs.tag }}"
+          TAG="${{ inputs.tag }}"
+          if [ -z "$TAG" ]; then
+            TAG="${{ github.event.inputs.tag }}"
+          fi
           if [ -z "$TAG" ]; then
             TAG=$(git ls-remote --tags --sort=-v:refname origin 'refs/tags/v*' | head -1 | sed 's|.*refs/tags/||')
           fi