Publish a Gitea Release from CI on every v* tag

Nothing made a release. CI built the APK and the installer on the master
push and kept them as workflow artefacts, the Linux binary was not kept
at all, and most tags went out with no downloads until they were
attached by hand.

build-and-test now also runs on v* tags. On a tag the desktop job keeps
its release binary, and a release job that needs desktop, Android and
Windows collects the three, names them with the version and runs
tools/publish-release.sh. The script titles and describes the release
from the annotated tag's message as the server holds it, writes
SHA256SUMS, and attaches what is not already there, so a re-run after
an interrupted upload finishes the job instead of duplicating it. The
same script is how a release is made or finished by hand.

Tried on v0.14.1, whose release was made by hand with the same files:
it found the release, reported all four files attached, and changed
nothing.

.gitea/workflows/build-and-test.yml

@@ -7,6 +7,10 @@ name: Build and test
 on:
   push:
     branches: [main, master, develop]
+    # A release tag builds again and publishes what it built (the `release`
+    # job at the end). The master push of the same commit has usually filled
+    # the caches, so the second run is the warm one.
+    tags: ['v*']
   pull_request:
     branches: [main, master, develop]
 
@@ -154,6 +158,16 @@ jobs:
       - name: Build
         run: cargo build --workspace --release
 
+      # Only on a release tag: the binary is 150 MB and nothing but the
+      # release job wants it.
+      - name: Upload the desktop binary
+        if: startsWith(github.ref, 'refs/tags/v')
+        uses: actions/upload-artifact@v3
+        with:
+          name: darkroom-desktop-x86_64-linux
+          path: target/release/darkroom-desktop
+          if-no-files-found: error
+
       - name: Disk after
         if: always()
         run: df -h /workspace 2>/dev/null || df -h .
@@ -519,3 +533,47 @@ jobs:
             fi
           done
           exit $FAILED
+
+  # A v* tag becomes a Gitea Release carrying the three builds and their
+  # SHA256SUMS, titled and described by the tag's message. Until this job
+  # existed every release was made by hand, and most tags never got one.
+  #
+  # It needs all three platform jobs, so a tag whose tests fail publishes
+  # nothing; re-run the failed job and this one follows. The work is
+  # tools/publish-release.sh, which is also how a release is finished by hand.
+  release:
+    if: startsWith(github.ref, 'refs/tags/v')
+    needs: [desktop, android, windows]
+    runs-on: linux/amd64
+    name: Publish the release
+    container:
+      image: catthehacker/ubuntu:act-latest
+    permissions:
+      contents: write
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Fetch the builds
+        uses: actions/download-artifact@v3
+        with:
+          path: dist
+
+      # Named for the download page, with the version in each name the way
+      # the hand-made releases had them. The installer already carries its
+      # version from package.sh.
+      - name: Publish
+        env:
+          GITEA_TOKEN: ${{ secrets.GITEA_TOKEN || github.token }}
+          TAG: ${{ github.ref_name }}
+        run: |
+          set -e
+          V="${TAG#v}"
+          ls -lR dist
+          mkdir -p out
+          cp dist/darkroom-arm64-v8a-apk/darkroom.apk "out/darkroom-${V}-arm64-v8a.apk"
+          cp dist/darkroom-desktop-x86_64-linux/darkroom-desktop "out/darkroom-desktop-${V}-x86_64-linux"
+          chmod +x "out/darkroom-desktop-${V}-x86_64-linux"
+          cp dist/darkroom-windows-x86_64-setup/DarkRoom-${V}-x86_64-setup.exe out/
+          bash tools/publish-release.sh "$TAG" out/*