Build infrastructure for releases

- Makefile: cross-compile to linux/{amd64,arm64}, darwin/{amd64,arm64},
  windows/amd64 into dist/ with SHA256SUMS. Version is stamped via
  -ldflags '-X main.version=...'.
- .gitea/workflows/release.yml: on tag push (v*) the workflow runs
  `make dist`, creates a Gitea release for the tag and uploads every
  artefact from dist/ via the Gitea API.
- main.go: `rb-search version` / --version prints the stamped version.
- README: new "Готовые бинари" section with curl/Invoke-WebRequest
  install snippets and a checksum-verify hint.

.gitea/workflows/release.yml

@@ -0,0 +1,51 @@
+name: release
+
+on:
+  push:
+    tags:
+      - 'v*'
+
+jobs:
+  release:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-go@v5
+        with:
+          go-version: '1.22'
+
+      - name: Build cross-platform binaries
+        run: make dist VERSION=${{ github.ref_name }}
+
+      - name: Create release and upload assets
+        env:
+          TOKEN: ${{ secrets.GITEA_TOKEN }}
+          API:   ${{ github.server_url }}/api/v1/repos/${{ github.repository }}
+          TAG:   ${{ github.ref_name }}
+        run: |
+          set -euo pipefail
+          body=$(cat <<EOF
+          Автоматический релиз $TAG.
+
+          Скачайте бинарь под свою ОС/архитектуру и положите на PATH.
+          Проверка целостности: \`sha256sum -c SHA256SUMS\`.
+          EOF
+          )
+          payload=$(jq -n --arg tag "$TAG" --arg body "$body" \
+            '{tag_name:$tag, name:$tag, body:$body, draft:false, prerelease:false}')
+          release_id=$(curl -fsSL -X POST \
+            -H "Authorization: token $TOKEN" \
+            -H "Content-Type: application/json" \
+            -d "$payload" \
+            "$API/releases" | jq -r .id)
+          for f in dist/*; do
+            name=$(basename "$f")
+            echo "uploading $name"
+            curl -fsSL -X POST \
+              -H "Authorization: token $TOKEN" \
+              -H "Content-Type: application/octet-stream" \
+              --data-binary "@$f" \
+              "$API/releases/$release_id/assets?name=$name" >/dev/null
+          done
+          echo "released $TAG with $(ls dist | wc -l) assets"