Coordinators now dispatch per-OS builds via API

Previously per-OS build workflows triggered on tag push events, but
Gitea doesn't fire events for tags pushed by other workflows. Now:

- release.yml dispatches build-app-{linux,windows,macos}.yml via
  the Gitea API after creating the tag and release
- sidecar-release.yml dispatches build-sidecar-{linux,windows,macos}.yml

Per-OS workflows changed from push+dispatch triggers to dispatch-only
with tag as a required input. To re-run a failed build for the same
version, just dispatch the specific OS workflow with the same tag --
upload logic replaces existing assets automatically.

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

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

@@ -1,14 +1,11 @@
 name: Build App (Windows)
 
 on:
-  push:
-    tags:
-      - 'v*'
   workflow_dispatch:
     inputs:
       tag:
         description: 'Release tag to build (e.g. v1.4.5)'
-        required: false
+        required: true
 
 jobs:
   build-windows:
@@ -21,20 +18,12 @@ jobs:
         id: tag
         shell: powershell
         run: |
-          $inputTag = "${{ github.event.inputs.tag }}"
-          $ref = "${{ github.ref }}"
-          $refName = "${{ github.ref_name }}"
-
-          if ($inputTag) {
-            $TAG = $inputTag
-          } elseif ($ref -like "refs/tags/*") {
-            $TAG = $refName
-          } else {
-            $tags = git ls-remote --tags --sort=-v:refname origin 'refs/tags/v*' 2>&1
-            $TAG = ($tags | Select-Object -First 1) -replace '.*refs/tags/', ''
+          $TAG = "${{ github.event.inputs.tag }}"
+          if (-not $TAG) {
+            $TAG = (git ls-remote --tags --sort=-v:refname origin 'refs/tags/v*' | Select-Object -First 1) -replace '.*refs/tags/', ''
           }
           Write-Host "Building for tag: ${TAG}"
-          echo "tag=${TAG}" | Out-File -FilePath $env:GITHUB_OUTPUT -Encoding utf8 -Append
+          echo "tag=${TAG}" >> $env:GITHUB_OUTPUT
 
       - uses: actions/checkout@v4
         with: