Packaging: the wheel carries the PWA, so a release install serves the UI (v2.7.10)

- pyproject declared build-backend = "setuptools.backends._legacy:_Backend",
  which does not exist: `python -m build`, `pip install .` and even
  `pip install -e .` died with "Backend ... is not available".  It is
  setuptools.build_meta now.
- the wheel and sdist carried only the Python packages, and _default_web_dir()
  resolved <site-packages>/../frontend, so an installed server started fine but
  answered every static request with 404.  setup.py's build_py now copies the
  checkout's frontend/ into simtrace_analyser/web/ inside the build (the PWA's
  tests excluded), and _default_web_dir() prefers that packaged copy, falling
  back to <repo>/frontend for source and editable runs.  The source directory
  is resolved from setup.py (so an sdist build works) and a missing frontend/
  fails the build loudly instead of shipping a package without its UI.
- MANIFEST.in grafts frontend/ (with the READMEs, the udev rule and the four
  launch scripts) into the sdist, so a wheel built from the sdist has the PWA.
- README (EN/RU): an install-from-a-release section (pipx/pip with the wheel,
  the direct release URL for pip) and the --web-dir default documented as the
  bundled PWA, or <repo>/frontend from source.
- tests/test_packaging.py pins the packaged-first resolution (including the
  empty-directory fallback), the source checkout default, the real build
  backend, the manifest graft and setup.py's bundling.
- verified: a fresh venv install from the wheel and from the sdist serve
  GET / (200, byte-identical index.html, PWA v2.7.10) out of
  site-packages/simtrace_analyser/web; an editable install still resolves
  <repo>/frontend.  547 Python + 80 Node tests.

README.md

@@ -108,12 +108,34 @@ pip install -e .
 # or:       simtrace2-pysniff [opts]
 ```
 
+### From a release (no git checkout)
+
+The release artifacts bundle the PWA, so an installed server serves the same UI
+as a clone.  Download the wheel from the
+[latest release](https://github.com/anttro/simtrace-analyser/releases/latest)
+and install it:
+
+```sh
+pipx install ./simtrace_analyser-2.7.10-py3-none-any.whl
+# or: pip install ./simtrace_analyser-2.7.10-py3-none-any.whl
+
+# then run (the UI is served at http://127.0.0.1:8081/):
+simtrace-analyser-server --capture gsmtap
+```
+
+`pip` can also fetch the wheel straight from the release page:
+
+```sh
+pip install https://github.com/anttro/simtrace-analyser/releases/download/v2.7.10/simtrace_analyser-2.7.10-py3-none-any.whl
+```
+
 ## Running
 
 ### Analysis server + PWA (`simtrace-analyser-server`)
 
 Stores captured APDU traffic in SQLite and serves it over HTTP, together with
-the bundled **SIMtrace Analyser** PWA (`frontend/`) on the same origin.  Three
+the bundled **SIMtrace Analyser** PWA (`frontend/` in a source checkout,
+bundled into the package on install) on the same origin.  Three
 capture modes:
 
 ```sh
@@ -283,13 +305,14 @@ Server options:
 --db FILE            SQLite database path (default: ~/.simtrace-analyser/sessions.db)
 --capture MODE       gsmtap | direct | disabled  (default: gsmtap)
 --gsmtap-port PORT   UDP port for the GSMTAP listener (default: 4729)
---web-dir PATH       PWA static files directory (default: <repo>/frontend)
+--web-dir PATH       PWA static files directory (default: the PWA bundled in
+                     the installed package, or <repo>/frontend from source)
 ```
 
 Then open **http://127.0.0.1:8081/** in a browser — the PWA is served by the
 server, so the UI and the API share an origin and no CORS/Private-Network-Access
 setup is involved.  Use `--web-dir PATH` to serve a different PWA directory
-(default: `<repo>/frontend`).
+(default: the bundled PWA, or `<repo>/frontend` in a source checkout).
 
 ### Hosted PWA (landing page)