Release packaging: archives, workflow, download-first docs, Windows notes

- tools/build_release.sh: builds the Linux tar.gz and Windows zip from a
  git ref (default HEAD) using an explicit `git archive` pathspec
  allowlist: decoder (__init__.py, pd.py, gsmtap_stream.py), setup/start
  scripts, tools/vs_reader.py, READMEs, LICENSE and the README-referenced
  resources/ images.  v* tags must match pd.py VERSION.  Both archives
  are listed and extracted and checked for VERSION, py_compile, bash -n,
  .bat CRLF / .sh LF and tar exec bits; SHA256SUMS uses sha256sum or
  shasum.  Builds into a staging dir and only then replaces dist/.
- .github/workflows/release.yml: on a v* tag push run the unit tests,
  verify tag == pd.py VERSION, build, then upload into an existing
  release or create a draft and publish it; release-<tag> concurrency.
- README/RUS: Installation documents both ways (release download
  recommended; source checkout for development), SHA256SUMS verification,
  and the Windows prerequisites verified against sigrok.org (0.7.2
  release installer as the tested version, nightly caveat, VC++ 2010
  redist, bundled fx2lafw firmware and Zadig, per-port driver binding).
- start.bat: accept --opt=value alongside the original --opt value form
  (the usage text advertised the = form while the parser required a
  space); usage corrected and notes the core subset.
- .gitignore: dist/.
- AGENTS: release packaging, build verification and release process
  (commit docs/workflow first, then tag and push, auto-generated notes).

No decoder behavior change; VERSION stays 1.9.7.

.github/workflows/release.yml

@@ -0,0 +1,63 @@
+name: release
+
+on:
+  push:
+    tags:
+      - 'v*'
+
+permissions:
+  contents: write
+
+concurrency:
+  group: release-${{ github.ref_name }}
+  cancel-in-progress: false
+
+jobs:
+  release:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - uses: actions/setup-python@v5
+        with:
+          python-version: '3.x'
+
+      - name: Unit tests
+        run: python3 tests/test_gsmtap.py
+
+      - name: Verify tag matches pd.py VERSION
+        shell: bash
+        run: |
+          set -euo pipefail
+          version=$(sed -n "s/^VERSION = '\([0-9][0-9.]*\)'.*/\1/p" pd.py)
+          if [ -z "$version" ]; then
+            echo "::error::cannot read VERSION from pd.py"
+            exit 1
+          fi
+          if [ "$GITHUB_REF_NAME" != "v$version" ]; then
+            echo "::error::tag $GITHUB_REF_NAME does not match pd.py VERSION '$version'"
+            exit 1
+          fi
+          echo "tag $GITHUB_REF_NAME matches pd.py VERSION $version"
+
+      - name: Build release archives
+        run: ./tools/build_release.sh "$GITHUB_REF_NAME"
+
+      - name: Create or update the GitHub release
+        shell: bash
+        env:
+          GH_TOKEN: ${{ github.token }}
+        run: |
+          set -euo pipefail
+          version=$(sed -n "s/^VERSION = '\([0-9][0-9.]*\)'.*/\1/p" pd.py)
+          # Upload into an existing release first.  If the release does not
+          # exist yet, create it as a draft so the published release never
+          # appears with a partial asset set.
+          if ! gh release upload "$GITHUB_REF_NAME" dist/* --clobber; then
+            gh release create "$GITHUB_REF_NAME" dist/* --draft \
+              --title "sigrok_iso7816_stream $version" --generate-notes
+          fi
+          # Publish a new draft and re-publish an existing one.
+          gh release edit "$GITHUB_REF_NAME" --draft=false