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.

tests/test_packaging.py

@@ -0,0 +1,83 @@
+"""Tests for the distributable packaging (bundled PWA, backend, manifest)."""
+
+import os
+import tempfile
+import unittest
+
+from simtrace_analyser.__main__ import _default_web_dir, _pick_web_dir
+
+REPO = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
+
+
+def _touch(path):
+    with open(path, 'w') as f:
+        f.write('')
+
+
+class TestPickWebDir(unittest.TestCase):
+    def test_prefers_packaged_pwa(self):
+        with tempfile.TemporaryDirectory() as tmp:
+            pkg = os.path.join(tmp, 'simtrace_analyser')
+            repo = os.path.join(tmp, 'repo')
+            os.makedirs(os.path.join(pkg, 'web'))
+            os.makedirs(os.path.join(repo, 'frontend'))
+            _touch(os.path.join(pkg, 'web', 'index.html'))
+            _touch(os.path.join(repo, 'frontend', 'index.html'))
+            self.assertEqual(_pick_web_dir(pkg, repo),
+                             os.path.join(pkg, 'web'))
+
+    def test_falls_back_when_packaged_dir_is_missing(self):
+        with tempfile.TemporaryDirectory() as tmp:
+            pkg = os.path.join(tmp, 'simtrace_analyser')
+            repo = os.path.join(tmp, 'repo')
+            os.makedirs(pkg)
+            os.makedirs(os.path.join(repo, 'frontend'))
+            _touch(os.path.join(repo, 'frontend', 'index.html'))
+            self.assertEqual(_pick_web_dir(pkg, repo),
+                             os.path.join(repo, 'frontend'))
+
+    def test_falls_back_when_packaged_dir_has_no_index(self):
+        # A stale/empty simtrace_analyser/web directory must not shadow the
+        # source checkout (e.g. an editable install of a half-built tree).
+        with tempfile.TemporaryDirectory() as tmp:
+            pkg = os.path.join(tmp, 'simtrace_analyser')
+            repo = os.path.join(tmp, 'repo')
+            os.makedirs(os.path.join(pkg, 'web'))
+            os.makedirs(os.path.join(repo, 'frontend'))
+            _touch(os.path.join(repo, 'frontend', 'index.html'))
+            self.assertEqual(_pick_web_dir(pkg, repo),
+                             os.path.join(repo, 'frontend'))
+
+
+class TestDefaultWebDir(unittest.TestCase):
+    def test_source_checkout(self):
+        web = _default_web_dir()
+        self.assertTrue(os.path.isfile(os.path.join(web, 'index.html')),
+                        'no index.html in %s' % web)
+
+
+class TestDistributionMetadata(unittest.TestCase):
+    def _read(self, name):
+        with open(os.path.join(REPO, name)) as f:
+            return f.read()
+
+    def test_build_backend_exists(self):
+        pyproject = self._read('pyproject.toml')
+        self.assertIn('build-backend = "setuptools.build_meta"', pyproject)
+        self.assertNotIn('backends._legacy', pyproject)
+
+    def test_manifest_ships_the_pwa(self):
+        # The sdist carries frontend/, so a wheel built from it has the PWA.
+        self.assertIn('graft frontend', self._read('MANIFEST.in'))
+
+    def test_setup_py_bundles_the_pwa(self):
+        setup_py = self._read('setup.py')
+        self.assertIn('frontend', setup_py)
+        self.assertIn('copytree', setup_py)
+        self.assertIn("'web'", setup_py)
+        self.assertIn("'build_py'", setup_py)
+        self.assertIn('ignore_patterns', setup_py)
+
+
+if __name__ == '__main__':
+    unittest.main()