feat(polls): complete the poll lifecycle — voting, undisclosed, end, spec-correct

Upgrade the MSC3381 poll feature from a leaky half-implementation to a complete,
cross-client-correct one:

- End/close a poll (creator or redact-PL mod) via inline confirm → m.poll.end;
  locks voting, reveals results, marks winner(s); only pre-end responses count.
- Honor poll kind: undisclosed polls hide counts/percent/bars/total until ended
  (creator gets a Show-live-results vs Hidden-until-ended toggle; default live).
  Previously every poll was created undisclosed yet the UI leaked live results.
- Enforce max_selections for multi-choice; radiogroup/checkbox a11y with arrow-key
  roving and an AT-announced winner.
- Robust, dual-namespace wire handling: parse BOTH stable (m.poll/m.id/m.selections)
  and unstable (org.matrix.msc3381.poll.*) by hand — matrix-js-sdk 41.7.0's
  PollStart/Response parsers only understand the unstable bodies, so delegating to
  them broke every stable poll (caught in agent review). Use the SDK Poll model only
  for end validation + before-end filtering.
- Pure tally/visibility/winner/parse logic extracted to utils/poll.ts with 14 tests
  incl. a stable/unstable wire-format round-trip.

Reviewed by 3 agents (spec/cross-client, logic, a11y/UI); findings applied.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

LOTUS_FEATURES.md

@@ -829,14 +829,21 @@ player.kick).
 
 ### Poll Creation
 
-- `PollCreator.tsx` creates stable `m.poll.start` events
-- Supports 2 to 10 answer options
-- Supports both single-choice and multiple-choice modes
+- `PollCreator.tsx` creates stable `m.poll.start` events (with a text fallback body for non-poll clients)
+- Supports 2 to 10 answer options; single-choice or multiple-choice
+- **Results visibility toggle** — _Show live results_ (disclosed, default) vs _Hidden until ended_ (undisclosed)
 - Accessible via the `Icons.OrderList` button in the composer toolbar
 
-### Poll Display
+### Poll Display & Voting (MSC3381, full lifecycle)
 
-`PollContent.tsx` renders polls in read-only mode. Handles both the stable `m.poll` format and the legacy MSC3381 unstable `org.matrix.msc3381.poll.start` format. Displays current vote counts and a note directing users to Element to cast votes.
+`PollContent.tsx` is a fully interactive, spec-correct poll card:
+
+- **Vote / change / clear** in place — sends stable `m.poll.response` (`m.selections`); latest response per voter wins; clearing removes you from the tally. Multi-choice enforces `max_selections` ("Select up to N").
+- **Disclosed vs undisclosed** — undisclosed polls hide counts/percentages/bars (and the vote total) until the poll ends; disclosed polls show live results.
+- **End a poll** — the poll's creator or a moderator (redact power) can end it via an inline confirm; sends stable `m.poll.end`. Ended polls lock voting, show "Poll closed · Final results", reveal results, and highlight the winner(s) (ties supported). Only responses cast on/before the end event count.
+- **Cross-client** — reads **both** the stable (`m.poll`/`m.id`/`m.selections`) and unstable (`org.matrix.msc3381.poll.*`) wire formats by hand (matrix-js-sdk 41.7.0's poll parsers only speak unstable), and uses the SDK `Poll` model for end-event validation (creator / redact-PL) + before-end response filtering. Polls authored in Element render/vote/end correctly and vice-versa.
+- **Accessibility** — `radiogroup`/`radio` (single, with arrow-key roving) or `group`/`checkbox` (multi) semantics, `aria-checked`/`aria-disabled`, winner announced to AT.
+- Pure tally/visibility/winner + wire-format parsing live in `utils/poll.ts` (+ `poll.test.ts`, 14 tests incl. the stable/unstable round-trip).
 
 ### Voice Message Playback Speed