Phase 5b and Phase 6: TypeScript restructure, jsdom tests, regex filters and per-playlist buffer in the UI

TypeScript:
- menu_ts.ts split into menu.ts, content.ts, popup.ts and xmltv.ts; the
  other files drop their _ts suffix. Bundle order fixed in ts/tsconfig.json.
- All 94 string event handlers (setAttribute("onclick", "javascript: ..."))
  replaced with addEventListener closures. changeButtonAction, which
  rewrote an onclick attribute from select values, is gone.
- Settings rows are generated from one SETTINGS_FIELDS table instead of
  ~20 copy-pasted blocks; rendered HTML is byte-identical to before.
  saveSettings now serialises password inputs, so a changed Plex token is
  actually sent (the server treats the mask as unchanged).
- createLayout rebuilds the menu list only when the set of visible items
  changes, so focus in the menu survives a refresh.
- announce()/alertUser(): alerts are mirrored into an aria-live region.
- Filter popup offers a third type, Regular Expression (regex-filter), and
  the filter table labels it. Playlist popups get a Buffer select
  (default / none / xTeVe / FFmpeg / VLC) saved as the playlist's
  "buffer" parameter; the tuner field stays editable when the
  playlist's own buffer is active.

Tests: tests/ holds 27 jsdom tests (Node's built-in runner, jsdom pinned)
that load the built bundle with a fixture server payload: menu visibility
rules, mapping table renders names as text, settings panel fields, popup
flows, sorting, bulk select, layout refresh keeps nodes, live region,
regex option, buffer select. npm test runs in the Drone webui-check step.
README-DEV documents the layout and the test workflow.

tasks/todo.md

@@ -1,7 +1,7 @@
 # xTeVe improvement checklist
 
 Detailed rationale, file references and effort estimates: `tasks/improvement-plan.md`.
-Status: Phases 0, 1, 2, 3 done on branch `improvements` (2026-09-26); Phase 5 in progress.
+Status: all phases done on branch `improvements` (2026-09-26). Open: the `agent.md` design-system reference (user decision) and two items kept by design (Host-derived URLs, no user roles).
 
 ## Phase 0: Hygiene
 - [x] `.gitignore` (`.gocache/`), deleted `.gocache/`, extended `.dockerignore`
@@ -59,18 +59,18 @@ Not planned (lineup is ~170 channels, decided 2026-09-25). See plan for the refe
 
 ## Phase 5: Frontend architecture
 - [x] Persistent websocket: one socket per page, queued requests with ids echoed by the server, 12 s per-request timeout, exponential-backoff reconnect, log-poll dedupe. Server keeps serving on one connection and closes it on exit (upstream leaked one open socket per request). Test: `TestWSServesMultipleCommandsPerConnection`
-- [ ] Section-level re-render instead of full `createLayout()`
-- [ ] Virtualised mapping table
-- [ ] Split `menu_ts.ts`; `addEventListener`; data-driven settings rows
-- [ ] Accessibility follow-ups; light theme via `prefers-color-scheme`
-- [ ] Consolidate CSS layers
+- [x] `createLayout()` rebuilds the menu list only when the set of visible items changes; client info and status cards refresh in place (jsdom test keeps the same nodes and focus)
+- [~] Virtualised mapping table skipped: ~170 channels render instantly, and sorting/search operate on DOM rows, so virtualisation would add risk for no gain (same reasoning as dropping Phase 4)
+- [x] `menu_ts.ts` split into `menu.ts`, `content.ts`, `popup.ts`, `xmltv.ts` (all `_ts` suffixes dropped); all 94 string `on*` handlers replaced by `addEventListener`; settings rows generated from `SETTINGS_FIELDS`; password fields now saved (Plex token); 27 jsdom tests under `tests/` run by `npm test` in CI
+- [x] Live-region announcements alongside alerts, `lang`, single h1, `<main>` landmark; light theme via `prefers-color-scheme` with `data-theme` override (contrast measured). `<input type=button>` kept because every button style keys on it
+- [x] CSS split into tokens / base / components / layout, every colour a token, `screen.css` removed
 
 ## Phase 6: Optional features
-- [ ] Regex filters
-- [ ] Per-playlist tuner limit and buffer choice
-- [ ] Bulk channel edit
-- [ ] Versioned backup/restore
-- [ ] Dummy EPG durations
+- [x] Regex filters: `regex-filter` type (validated on save, cached compile, matches name, then group, then raw line) with a popup form and table label; tested in Go and jsdom
+- [x] Per-playlist tuner limit already existed. Per-playlist buffer: `buffer` select in the playlist popup (default / none / xTeVe / FFmpeg / VLC) backed by `bufferModeFor`; tuner field stays editable when the playlist's own buffer is active
+- [x] Already present in the fork (bulk edit with shift-range selection); nothing to add
+- [x] Already present: restore checks the backup's version against `System.Compatibility`; writes are now atomic (Phase 2)
+- [x] Already present: `xTeVe Dummy` offers several durations in the mapping dropdown
 
 ## Review