release: use public Gitea URL for user-facing artefact links

`github.server_url` on Gitea Actions resolves to the runner's
internal Gitea endpoint (e.g. http://gitea:3000) — fine for API
calls the runner makes itself, broken for URLs end-user machines
have to resolve. Both v0.1.0 user-facing places used it:

  - latest.json's `url` and `zsync` fields (read by AppImageUpdate
    on user machines).
  - The AppImage's embedded `--update-info` ELF section (also read
    by AppImageUpdate to find the appcast).

Result: v0.1.0's latest.json shipped pointing at gitea:3000, which
no end-user machine can reach.

Fix: add a job-level `PUBLIC_REPO_URL` env var (single source of
truth, easy to change if Gitea ever moves) and use it for both
artefact-URL composition sites. The release-create + asset-upload
API calls keep using `github.server_url`/`api/v1` — those are
runner→Gitea internal traffic where the internal URL is correct.

Note: v0.1.0's already-uploaded latest.json still has the broken
URLs. Either leave it (no auto-update consumers yet) or PATCH the
asset out of band; future tags will be correct once this lands.

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

.gitea/workflows/release.yml

@@ -10,6 +10,15 @@ jobs:
     name: Linux AppImage
     runs-on: ubuntu-latest
 
+    env:
+      # Public-facing repo URL for assets users will download.
+      # `github.server_url` resolves to the runner's internal Gitea
+      # endpoint (e.g. http://gitea:3000), which works for API calls
+      # the runner makes itself but not for URLs baked into latest.json
+      # or the AppImage's embedded --update-info — those are read by
+      # end-user machines that can only reach Gitea via its public URL.
+      PUBLIC_REPO_URL: 'https://src.bundespruefstelle.ch/magdev/php-qml'
+
     steps:
       - name: Checkout
         uses: actions/checkout@v4
@@ -64,7 +73,7 @@ jobs:
           # AppImageUpdate sidecar will fetch this .zsync URL; it must
           # point at the asset we're about to upload to this Release.
           APPIMAGE_UPDATE_INFO: |
-            zsync|${{ github.server_url }}/${{ github.repository }}/releases/download/${{ github.ref_name }}/Todo-x86_64.AppImage.zsync
+            zsync|${{ env.PUBLIC_REPO_URL }}/releases/download/${{ github.ref_name }}/Todo-x86_64.AppImage.zsync
         run: make appimage
 
       - name: Install zsync + Xvfb
@@ -103,7 +112,7 @@ jobs:
         run: |
           SIZE=$(stat -c %s Todo-x86_64.AppImage)
           SHA=$(sha256sum Todo-x86_64.AppImage | awk '{print $1}')
-          URL_BASE="${{ github.server_url }}/${{ github.repository }}/releases/download/${TAG}"
+          URL_BASE="${PUBLIC_REPO_URL}/releases/download/${TAG}"
           jq -n \
             --arg version "$TAG" \
             --arg url     "$URL_BASE/Todo-x86_64.AppImage" \