ci: add multi-platform release build via Gitea Actions

Builds tea for linux/amd64, linux/arm64, darwin/amd64, darwin/arm64 and
windows/amd64 on tag push and publishes them as a Gitea release.

.gitea/workflows/release.yml

@@ -0,0 +1,65 @@
+name: release
+
+on:
+  push:
+    tags:
+      - 'v*'
+  workflow_dispatch:
+
+permissions:
+  contents: write
+  releases: write
+
+jobs:
+  release:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+      - uses: actions/setup-go@v5
+        with:
+          go-version-file: go.mod
+      - name: build
+        run: |
+          set -e
+          VERSION="${GITHUB_REF_NAME#v}"
+          SDK="$(go list -f '{{.Version}}' -m gitea.dev/sdk)"
+          mkdir -p dist
+          for target in "linux amd64" "linux arm64" "darwin amd64" "darwin arm64" "windows amd64"; do
+            GOOS="${target% *}"
+            GOARCH="${target#* }"
+            EXT=""
+            if [ "$GOOS" = "windows" ]; then EXT=".exe"; fi
+            GOOS="$GOOS" GOARCH="$GOARCH" CGO_ENABLED=0 go build -trimpath \
+              -ldflags "-X 'gitea.dev/tea/modules/version.Version=${VERSION}' -X 'gitea.dev/tea/modules/version.SDK=${SDK}' -s -w" \
+              -o "dist/tea-${GOOS}-${GOARCH}${EXT}" .
+          done
+          cd dist
+          for f in tea-*; do
+            sha256sum "$f" > "$f.sha256"
+          done
+      - uses: actions/upload-artifact@v4
+        with:
+          name: tea-binaries
+          path: dist/*
+          if-no-files-found: error
+      - name: create release + upload assets
+        env:
+          GITEA_TOKEN: ${{ secrets.GITEA_TOKEN }}
+        run: |
+          set -e
+          TAG="${GITHUB_REF_NAME}"
+          API="${GITHUB_SERVER_URL}/api/v1/repos/${GITHUB_REPOSITORY}"
+          RESPONSE="$(curl -sf -X POST \
+            -H "Authorization: token ${GITEA_TOKEN}" \
+            -H "Content-Type: application/json" \
+            "${API}/releases" \
+            -d "{\"tag_name\":\"${TAG}\",\"name\":\"${TAG}\"}")"
+          RELEASE_ID="$(printf '%s' "$RESPONSE" | python3 -c 'import sys,json;print(json.load(sys.stdin)["id"])')"
+          for f in dist/tea-*; do
+            curl -sf -X POST \
+              -H "Authorization: token ${GITEA_TOKEN}" \
+              -F "attachment=@${f}" \
+              "${API}/releases/${RELEASE_ID}/assets" >/dev/null
+          done