feat: split the web UI into modules and rework it for screen readers

webui.html becomes webui/ (index.html, style.css, ES modules in js/, no
build step); web.py serves it under / and /ui/<path> with the same
containment check as recordings.

How it feels with a screen reader:
- Days read "Today, Saturday 17 October"; recordings are named by their
  wall-clock span ("22:00 to 23:00"), which is the row header and what
  every button says. The filename moves to the last column.
- Focus is never dropped: busy buttons stay focused (aria-disabled),
  finished analyses focus their first section, delete moves to the next
  row, closing the clip bar (x or Escape) returns to where you were.
- Reloads rebuild only the days whose content changed; DOM ids are stable
  per filename, so a rollover no longer resets the reading position.
- Only user-initiated actions are announced; highlights completion is
  spoken (the progress area was stuck aria-busy before).
- Media Session previous/next track step sections like J/K (AirPods,
  lock screen, media keys).
- Row layout: Time | Length | Loudness | Player | Options | File. The
  player opens inside its cell; Download/Cut/Delete are always there,
  and Cut toggles its start/end fields in place.
- Settings tucked behind a <details>; pre-roll and auto-advance are
  remembered per browser; no CSS uppercase on headers or badges.

Fixes the REC badge showing on every row: its inline-flex display beat
the UA [hidden] rule. One global [hidden]{display:none !important} now
covers every case.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/test_web.py

@@ -75,3 +75,43 @@ def test_clip_failure_before_headers_still_reports_json(tmp_path, write_wav):
     assert h.close_connection is False
     assert h.codes == [500]
     assert b'could not open' in h.wfile.getvalue()
+
+
+# ---------------------------------------------------------------------------
+# Browser UI static files (webui/)
+# ---------------------------------------------------------------------------
+
+def test_ui_serves_index_and_modules_with_their_types(tmp_path):
+    h = _OfflineHandler(tmp_path)
+    types = []
+    h.send_header = lambda key, value: types.append(value) if key == 'Content-Type' else None
+
+    h._ui('index.html')
+    h._ui('js/main.js')
+    h._ui('style.css')
+
+    assert h.codes == [200, 200, 200]
+    assert types == ['text/html; charset=utf-8', 'text/javascript; charset=utf-8',
+                     'text/css; charset=utf-8']
+
+
+def test_ui_refuses_paths_outside_webui_and_unlisted_types(tmp_path):
+    h = _OfflineHandler(tmp_path)
+
+    h._ui('../web.py')           # escapes webui/
+    h._ui('..\web.py')
+    h._ui('js')                  # a directory
+    h._ui('missing.js')
+
+    assert h.codes == [404, 404, 404, 404]
+    assert b'import' not in h.wfile.getvalue()
+
+
+def test_every_ui_module_import_resolves():
+    # No JS toolchain on the dev box: at least catch a renamed module or a
+    # misspelt relative import before the browser does.
+    import re
+    js = web.WEBUI_DIR / 'js'
+    for mod in js.glob('*.js'):
+        for target in re.findall(r"from '\./([\w.]+)'", mod.read_text(encoding='utf-8')):
+            assert (js / target).is_file(), f'{mod.name} imports missing {target}'